localforage/dist/localforage.nopromises.js

/*!
    localForage -- Offline Storage, Improved
    Version 1.5.4
    https://localforage.github.io/localForage
    (c) 2013-2017 Mozilla, Apache License 2.0
*/
(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.localforage = f()}})(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw (f.code="MODULE_NOT_FOUND", f)}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(_dereq_,module,exports){
'use strict';

var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol" ? function (obj) { return typeof obj; } : function (obj) { return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj; };

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

function getIDB() {
    /* global indexedDB,webkitIndexedDB,mozIndexedDB,OIndexedDB,msIndexedDB */
    try {
        if (typeof indexedDB !== 'undefined') {
            return indexedDB;
        }
        if (typeof webkitIndexedDB !== 'undefined') {
            return webkitIndexedDB;
        }
        if (typeof mozIndexedDB !== 'undefined') {
            return mozIndexedDB;
        }
        if (typeof OIndexedDB !== 'undefined') {
            return OIndexedDB;
        }
        if (typeof msIndexedDB !== 'undefined') {
            return msIndexedDB;
        }
    } catch (e) {
        return;
    }
}

var idb = getIDB();

function isIndexedDBValid() {
    try {
        // Initialize IndexedDB; fall back to vendor-prefixed versions
        // if needed.
        if (!idb) {
            return false;
        }
        // We mimic PouchDB here;
        //
        // We test for openDatabase because IE Mobile identifies itself
        // as Safari. Oh the lulz...
        var isSafari = typeof openDatabase !== 'undefined' && /(Safari|iPhone|iPad|iPod)/.test(navigator.userAgent) && !/Chrome/.test(navigator.userAgent) && !/BlackBerry/.test(navigator.platform);

        var hasFetch = typeof fetch === 'function' && fetch.toString().indexOf('[native code') !== -1;

        // Safari <10.1 does not meet our requirements for IDB support (#5572)
        // since Safari 10.1 shipped with fetch, we can use that to detect it
        return (!isSafari || hasFetch) && typeof indexedDB !== 'undefined' &&
        // some outdated implementations of IDB that appear on Samsung
        // and HTC Android devices <4.4 are missing IDBKeyRange
        // See: https://github.com/mozilla/localForage/issues/128
        // See: https://github.com/mozilla/localForage/issues/272
        typeof IDBKeyRange !== 'undefined';
    } catch (e) {
        return false;
    }
}

// Abstracts constructing a Blob object, so it also works in older
// browsers that don't support the native Blob constructor. (i.e.
// old QtWebKit versions, at least).
// Abstracts constructing a Blob object, so it also works in older
// browsers that don't support the native Blob constructor. (i.e.
// old QtWebKit versions, at least).
function createBlob(parts, properties) {
    /* global BlobBuilder,MSBlobBuilder,MozBlobBuilder,WebKitBlobBuilder */
    parts = parts || [];
    properties = properties || {};
    try {
        return new Blob(parts, properties);
    } catch (e) {
        if (e.name !== 'TypeError') {
            throw e;
        }
        var Builder = typeof BlobBuilder !== 'undefined' ? BlobBuilder : typeof MSBlobBuilder !== 'undefined' ? MSBlobBuilder : typeof MozBlobBuilder !== 'undefined' ? MozBlobBuilder : WebKitBlobBuilder;
        var builder = new Builder();
        for (var i = 0; i < parts.length; i += 1) {
            builder.append(parts[i]);
        }
        return builder.getBlob(properties.type);
    }
}

// This is CommonJS because lie is an external dependency, so Rollup
// can just ignore it.
if (typeof Promise === 'undefined') {
    // In the "nopromises" build this will just throw if you don't have
    // a global promise object, but it would throw anyway later.
    _dereq_('lie/polyfill');
}
var Promise$1 = Promise;

function executeCallback(promise, callback) {
    if (callback) {
        promise.then(function (result) {
            callback(null, result);
        }, function (error) {
            callback(error);
        });
    }
}

function executeTwoCallbacks(promise, callback, errorCallback) {
    if (typeof callback === 'function') {
        promise.then(callback);
    }

    if (typeof errorCallback === 'function') {
        promise["catch"](errorCallback);
    }
}

function normalizeKey(key) {
    // Cast the key to a string, as that's all we can set as a key.
    if (typeof key !== 'string') {
        console.warn(key + ' used as a key, but it is not a string.');
        key = String(key);
    }

    return key;
}

function getCallback() {
    if (arguments.length && typeof arguments[arguments.length - 1] === 'function') {
        return arguments[arguments.length - 1];
    }
}

// Some code originally from async_storage.js in
// [Gaia](https://github.com/mozilla-b2g/gaia).

var DETECT_BLOB_SUPPORT_STORE = 'local-forage-detect-blob-support';
var supportsBlobs;
var dbContexts;
var toString = Object.prototype.toString;

// Transaction Modes
var READ_ONLY = 'readonly';
var READ_WRITE = 'readwrite';

// Transform a binary string to an array buffer, because otherwise
// weird stuff happens when you try to work with the binary string directly.
// It is known.
// From http://stackoverflow.com/questions/14967647/ (continues on next line)
// encode-decode-image-with-base64-breaks-image (2013-04-21)
function _binStringToArrayBuffer(bin) {
    var length = bin.length;
    var buf = new ArrayBuffer(length);
    var arr = new Uint8Array(buf);
    for (var i = 0; i < length; i++) {
        arr[i] = bin.charCodeAt(i);
    }
    return buf;
}

//
// Blobs are not supported in all versions of IndexedDB, notably
// Chrome <37 and Android <5. In those versions, storing a blob will throw.
//
// Various other blob bugs exist in Chrome v37-42 (inclusive).
// Detecting them is expensive and confusing to users, and Chrome 37-42
// is at very low usage worldwide, so we do a hacky userAgent check instead.
//
// content-type bug: https://code.google.com/p/chromium/issues/detail?id=408120
// 404 bug: https://code.google.com/p/chromium/issues/detail?id=447916
// FileReader bug: https://code.google.com/p/chromium/issues/detail?id=447836
//
// Code borrowed from PouchDB. See:
// https://github.com/pouchdb/pouchdb/blob/master/packages/node_modules/pouchdb-adapter-idb/src/blobSupport.js
//
function _checkBlobSupportWithoutCaching(idb) {
    return new Promise$1(function (resolve) {
        var txn = idb.transaction(DETECT_BLOB_SUPPORT_STORE, READ_WRITE);
        var blob = createBlob(['']);
        txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob, 'key');

        txn.onabort = function (e) {
            // If the transaction aborts now its due to not being able to
            // write to the database, likely due to the disk being full
            e.preventDefault();
            e.stopPropagation();
            resolve(false);
        };

        txn.oncomplete = function () {
            var matchedChrome = navigator.userAgent.match(/Chrome\/(\d+)/);
            var matchedEdge = navigator.userAgent.match(/Edge\//);
            // MS Edge pretends to be Chrome 42:
            // https://msdn.microsoft.com/en-us/library/hh869301%28v=vs.85%29.aspx
            resolve(matchedEdge || !matchedChrome || parseInt(matchedChrome[1], 10) >= 43);
        };
    })["catch"](function () {
        return false; // error, so assume unsupported
    });
}

function _checkBlobSupport(idb) {
    if (typeof supportsBlobs === 'boolean') {
        return Promise$1.resolve(supportsBlobs);
    }
    return _checkBlobSupportWithoutCaching(idb).then(function (value) {
        supportsBlobs = value;
        return supportsBlobs;
    });
}

function _deferReadiness(dbInfo) {
    var dbContext = dbContexts[dbInfo.name];

    // Create a deferred object representing the current database operation.
    var deferredOperation = {};

    deferredOperation.promise = new Promise$1(function (resolve, reject) {
        deferredOperation.resolve = resolve;
        deferredOperation.reject = reject;
    });

    // Enqueue the deferred operation.
    dbContext.deferredOperations.push(deferredOperation);

    // Chain its promise to the database readiness.
    if (!dbContext.dbReady) {
        dbContext.dbReady = deferredOperation.promise;
    } else {
        dbContext.dbReady = dbContext.dbReady.then(function () {
            return deferredOperation.promise;
        });
    }
}

function _advanceReadiness(dbInfo) {
    var dbContext = dbContexts[dbInfo.name];

    // Dequeue a deferred operation.
    var deferredOperation = dbContext.deferredOperations.pop();

    // Resolve its promise (which is part of the database readiness
    // chain of promises).
    if (deferredOperation) {
        deferredOperation.resolve();
        return deferredOperation.promise;
    }
}

function _rejectReadiness(dbInfo, err) {
    var dbContext = dbContexts[dbInfo.name];

    // Dequeue a deferred operation.
    var deferredOperation = dbContext.deferredOperations.pop();

    // Reject its promise (which is part of the database readiness
    // chain of promises).
    if (deferredOperation) {
        deferredOperation.reject(err);
        return deferredOperation.promise;
    }
}

function _getConnection(dbInfo, upgradeNeeded) {
    return new Promise$1(function (resolve, reject) {

        if (dbInfo.db) {
            if (upgradeNeeded) {
                _deferReadiness(dbInfo);
                dbInfo.db.close();
            } else {
                return resolve(dbInfo.db);
            }
        }

        var dbArgs = [dbInfo.name];

        if (upgradeNeeded) {
            dbArgs.push(dbInfo.version);
        }

        var openreq = idb.open.apply(idb, dbArgs);

        if (upgradeNeeded) {
            openreq.onupgradeneeded = function (e) {
                var db = openreq.result;
                try {
                    db.createObjectStore(dbInfo.storeName);
                    if (e.oldVersion <= 1) {
                        // Added when support for blob shims was added
                        db.createObjectStore(DETECT_BLOB_SUPPORT_STORE);
                    }
                } catch (ex) {
                    if (ex.name === 'ConstraintError') {
                        console.warn('The database "' + dbInfo.name + '"' + ' has been upgraded from version ' + e.oldVersion + ' to version ' + e.newVersion + ', but the storage "' + dbInfo.storeName + '" already exists.');
                    } else {
                        throw ex;
                    }
                }
            };
        }

        openreq.onerror = function (e) {
            e.preventDefault();
            reject(openreq.error);
        };

        openreq.onsuccess = function () {
            resolve(openreq.result);
            _advanceReadiness(dbInfo);
        };
    });
}

function _getOriginalConnection(dbInfo) {
    return _getConnection(dbInfo, false);
}

function _getUpgradedConnection(dbInfo) {
    return _getConnection(dbInfo, true);
}

function _isUpgradeNeeded(dbInfo, defaultVersion) {
    if (!dbInfo.db) {
        return true;
    }

    var isNewStore = !dbInfo.db.objectStoreNames.contains(dbInfo.storeName);
    var isDowngrade = dbInfo.version < dbInfo.db.version;
    var isUpgrade = dbInfo.version > dbInfo.db.version;

    if (isDowngrade) {
        // If the version is not the default one
        // then warn for impossible downgrade.
        if (dbInfo.version !== defaultVersion) {
            console.warn('The database "' + dbInfo.name + '"' + ' can\'t be downgraded from version ' + dbInfo.db.version + ' to version ' + dbInfo.version + '.');
        }
        // Align the versions to prevent errors.
        dbInfo.version = dbInfo.db.version;
    }

    if (isUpgrade || isNewStore) {
        // If the store is new then increment the version (if needed).
        // This will trigger an "upgradeneeded" event which is required
        // for creating a store.
        if (isNewStore) {
            var incVersion = dbInfo.db.version + 1;
            if (incVersion > dbInfo.version) {
                dbInfo.version = incVersion;
            }
        }

        return true;
    }

    return false;
}

// encode a blob for indexeddb engines that don't support blobs
function _encodeBlob(blob) {
    return new Promise$1(function (resolve, reject) {
        var reader = new FileReader();
        reader.onerror = reject;
        reader.onloadend = function (e) {
            var base64 = btoa(e.target.result || '');
            resolve({
                __local_forage_encoded_blob: true,
                data: base64,
                type: blob.type
            });
        };
        reader.readAsBinaryString(blob);
    });
}

// decode an encoded blob
function _decodeBlob(encodedBlob) {
    var arrayBuff = _binStringToArrayBuffer(atob(encodedBlob.data));
    return createBlob([arrayBuff], { type: encodedBlob.type });
}

// is this one of our fancy encoded blobs?
function _isEncodedBlob(value) {
    return value && value.__local_forage_encoded_blob;
}

// Specialize the default `ready()` function by making it dependent
// on the current database operations. Thus, the driver will be actually
// ready when it's been initialized (default) *and* there are no pending
// operations on the database (initiated by some other instances).
function _fullyReady(callback) {
    var self = this;

    var promise = self._initReady().then(function () {
        var dbContext = dbContexts[self._dbInfo.name];

        if (dbContext && dbContext.dbReady) {
            return dbContext.dbReady;
        }
    });

    executeTwoCallbacks(promise, callback, callback);
    return promise;
}

// Try to establish a new db connection to replace the
// current one which is broken (i.e. experiencing
// InvalidStateError while creating a transaction).
function _tryReconnect(dbInfo) {
    _deferReadiness(dbInfo);

    var dbContext = dbContexts[dbInfo.name];
    var forages = dbContext.forages;

    for (var i = 0; i < forages.length; i++) {
        var forage = forages[i];
        if (forage._dbInfo.db) {
            forage._dbInfo.db.close();
            forage._dbInfo.db = null;
        }
    }

    return _getOriginalConnection(dbInfo).then(function (db) {
        for (var j = 0; j < forages.length; j++) {
            forages[j]._dbInfo.db = db;
        }
        dbInfo.db = db;
    }).then(function () {
        if (_isUpgradeNeeded(dbInfo)) {
            // Reopen the database for upgrading.
            return _getUpgradedConnection(dbInfo);
        }
    })["catch"](function (err) {
        _rejectReadiness(dbInfo, err);
        throw err;
    });
}

// FF doesn't like Promises (micro-tasks) and IDDB store operations,
// so we have to do it with callbacks
function createTransaction(dbInfo, mode, callback, retries) {
    if (retries === undefined) {
        retries = 1;
    }

    try {
        var tx = dbInfo.db.transaction(dbInfo.storeName, mode);
        callback(null, tx);
    } catch (err) {
        if (retries > 0 && (!dbInfo.db || err.name === 'InvalidStateError' || err.name === 'NotFoundError')) {

            return Promise$1.resolve().then(function () {
                if (!dbInfo.db || err.name === 'NotFoundError' && !dbInfo.db.objectStoreNames.contains(dbInfo.storeName) && dbInfo.version <= dbInfo.db.version) {
                    // increase the db version, to create the new ObjectStore
                    if (dbInfo.db) {
                        dbInfo.version = dbInfo.db.version + 1;
                    }
                    // Reopen the database for upgrading.
                    return _getUpgradedConnection(dbInfo);
                }
            }).then(function () {
                return _tryReconnect(dbInfo).then(function () {
                    createTransaction(dbInfo, mode, callback, retries - 1);
                });
            })["catch"](callback);
        }

        callback(err);
    }
}

// Open the IndexedDB database (automatically creates one if one didn't
// previously exist), using any options set in the config.
function _initStorage(options) {
    var self = this;
    var dbInfo = {
        db: null
    };

    if (options) {
        for (var i in options) {
            dbInfo[i] = options[i];
        }
    }

    // Initialize a singleton container for all running localForages.
    if (!dbContexts) {
        dbContexts = {};
    }

    // Get the current context of the database;
    var dbContext = dbContexts[dbInfo.name];

    // ...or create a new context.
    if (!dbContext) {
        dbContext = {
            // Running localForages sharing a database.
            forages: [],
            // Shared database.
            db: null,
            // Database readiness (promise).
            dbReady: null,
            // Deferred operations on the database.
            deferredOperations: []
        };
        // Register the new context in the global container.
        dbContexts[dbInfo.name] = dbContext;
    }

    // Register itself as a running localForage in the current context.
    dbContext.forages.push(self);

    // Replace the default `ready()` function with the specialized one.
    if (!self._initReady) {
        self._initReady = self.ready;
        self.ready = _fullyReady;
    }

    // Create an array of initialization states of the related localForages.
    var initPromises = [];

    function ignoreErrors() {
        // Don't handle errors here,
        // just makes sure related localForages aren't pending.
        return Promise$1.resolve();
    }

    for (var j = 0; j < dbContext.forages.length; j++) {
        var forage = dbContext.forages[j];
        if (forage !== self) {
            // Don't wait for itself...
            initPromises.push(forage._initReady()["catch"](ignoreErrors));
        }
    }

    // Take a snapshot of the related localForages.
    var forages = dbContext.forages.slice(0);

    // Initialize the connection process only when
    // all the related localForages aren't pending.
    return Promise$1.all(initPromises).then(function () {
        dbInfo.db = dbContext.db;
        // Get the connection or open a new one without upgrade.
        return _getOriginalConnection(dbInfo);
    }).then(function (db) {
        dbInfo.db = db;
        if (_isUpgradeNeeded(dbInfo, self._defaultConfig.version)) {
            // Reopen the database for upgrading.
            return _getUpgradedConnection(dbInfo);
        }
        return db;
    }).then(function (db) {
        dbInfo.db = dbContext.db = db;
        self._dbInfo = dbInfo;
        // Share the final connection amongst related localForages.
        for (var k = 0; k < forages.length; k++) {
            var forage = forages[k];
            if (forage !== self) {
                // Self is already up-to-date.
                forage._dbInfo.db = dbInfo.db;
                forage._dbInfo.version = dbInfo.version;
            }
        }
    });
}

function getItem(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_ONLY, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var req = store.get(key);

                    req.onsuccess = function () {
                        var value = req.result;
                        if (value === undefined) {
                            value = null;
                        }
                        if (_isEncodedBlob(value)) {
                            value = _decodeBlob(value);
                        }
                        resolve(value);
                    };

                    req.onerror = function () {
                        reject(req.error);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

// Iterate over all items stored in database.
function iterate(iterator, callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_ONLY, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var req = store.openCursor();
                    var iterationNumber = 1;

                    req.onsuccess = function () {
                        var cursor = req.result;

                        if (cursor) {
                            var value = cursor.value;
                            if (_isEncodedBlob(value)) {
                                value = _decodeBlob(value);
                            }
                            var result = iterator(value, cursor.key, iterationNumber++);

                            // when the iterator callback retuns any
                            // (non-`undefined`) value, then we stop
                            // the iteration immediately
                            if (result !== void 0) {
                                resolve(result);
                            } else {
                                cursor["continue"]();
                            }
                        } else {
                            resolve();
                        }
                    };

                    req.onerror = function () {
                        reject(req.error);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);

    return promise;
}

function setItem(key, value, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        var dbInfo;
        self.ready().then(function () {
            dbInfo = self._dbInfo;
            if (toString.call(value) === '[object Blob]') {
                return _checkBlobSupport(dbInfo.db).then(function (blobSupport) {
                    if (blobSupport) {
                        return value;
                    }
                    return _encodeBlob(value);
                });
            }
            return value;
        }).then(function (value) {
            createTransaction(self._dbInfo, READ_WRITE, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);

                    // The reason we don't _save_ null is because IE 10 does
                    // not support saving the `null` type in IndexedDB. How
                    // ironic, given the bug below!
                    // See: https://github.com/mozilla/localForage/issues/161
                    if (value === null) {
                        value = undefined;
                    }

                    var req = store.put(value, key);

                    transaction.oncomplete = function () {
                        // Cast to undefined so the value passed to
                        // callback/promise is the same as what one would get out
                        // of `getItem()` later. This leads to some weirdness
                        // (setItem('foo', undefined) will return `null`), but
                        // it's not my fault localStorage is our baseline and that
                        // it's weird.
                        if (value === undefined) {
                            value = null;
                        }

                        resolve(value);
                    };
                    transaction.onabort = transaction.onerror = function () {
                        var err = req.error ? req.error : req.transaction.error;
                        reject(err);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function removeItem(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_WRITE, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    // We use a Grunt task to make this safe for IE and some
                    // versions of Android (including those used by Cordova).
                    // Normally IE won't like `.delete()` and will insist on
                    // using `['delete']()`, but we have a build step that
                    // fixes this for us now.
                    var req = store["delete"](key);
                    transaction.oncomplete = function () {
                        resolve();
                    };

                    transaction.onerror = function () {
                        reject(req.error);
                    };

                    // The request will be also be aborted if we've exceeded our storage
                    // space.
                    transaction.onabort = function () {
                        var err = req.error ? req.error : req.transaction.error;
                        reject(err);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function clear(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_WRITE, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var req = store.clear();

                    transaction.oncomplete = function () {
                        resolve();
                    };

                    transaction.onabort = transaction.onerror = function () {
                        var err = req.error ? req.error : req.transaction.error;
                        reject(err);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function length(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_ONLY, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var req = store.count();

                    req.onsuccess = function () {
                        resolve(req.result);
                    };

                    req.onerror = function () {
                        reject(req.error);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function key(n, callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        if (n < 0) {
            resolve(null);

            return;
        }

        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_ONLY, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var advanced = false;
                    var req = store.openCursor();

                    req.onsuccess = function () {
                        var cursor = req.result;
                        if (!cursor) {
                            // this means there weren't enough keys
                            resolve(null);

                            return;
                        }

                        if (n === 0) {
                            // We have the first key, return it if that's what they
                            // wanted.
                            resolve(cursor.key);
                        } else {
                            if (!advanced) {
                                // Otherwise, ask the cursor to skip ahead n
                                // records.
                                advanced = true;
                                cursor.advance(n);
                            } else {
                                // When we get here, we've got the nth key.
                                resolve(cursor.key);
                            }
                        }
                    };

                    req.onerror = function () {
                        reject(req.error);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function keys(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            createTransaction(self._dbInfo, READ_ONLY, function (err, transaction) {
                if (err) {
                    return reject(err);
                }

                try {
                    var store = transaction.objectStore(self._dbInfo.storeName);
                    var req = store.openCursor();
                    var keys = [];

                    req.onsuccess = function () {
                        var cursor = req.result;

                        if (!cursor) {
                            resolve(keys);
                            return;
                        }

                        keys.push(cursor.key);
                        cursor["continue"]();
                    };

                    req.onerror = function () {
                        reject(req.error);
                    };
                } catch (e) {
                    reject(e);
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function dropInstance(options, callback) {
    callback = getCallback.apply(this, arguments);

    var currentConfig = this.config();
    options = typeof options !== 'function' && options || {};
    if (!options.name) {
        options.name = options.name || currentConfig.name;
        options.storeName = options.storeName || currentConfig.storeName;
    }

    var self = this;
    var promise;
    if (!options.name) {
        promise = Promise$1.reject('Invalid arguments');
    } else {
        var dbPromise = options.name === currentConfig.name && self._dbInfo.db ? Promise$1.resolve(self._dbInfo.db) : _getOriginalConnection(options);

        if (!options.storeName) {
            promise = dbPromise.then(function () {

                _deferReadiness(options);

                var dbContext = dbContexts[options.name];
                var forages = dbContext.forages;

                for (var i = 0; i < forages.length; i++) {
                    var forage = forages[i];
                    if (forage._dbInfo.db) {
                        forage._dbInfo.db.close();
                        forage._dbInfo.db = null;
                    }
                }

                var dropDBPromise = new Promise$1(function (resolve, reject) {
                    var req = idb.deleteDatabase(options.name);

                    req.onerror = req.onblocked = reject;

                    req.onsuccess = resolve;
                });

                return dropDBPromise.then(function () {
                    for (var j = 0; j < forages.length; j++) {
                        _advanceReadiness(forage._dbInfo);
                    }
                })["catch"](function (err) {
                    (_rejectReadiness(options, err) || Promise$1.resolve())["catch"](function () {});
                    throw err;
                });
            });
        } else {
            promise = dbPromise.then(function (db) {
                if (!db.objectStoreNames.contains(options.storeName)) {
                    return;
                }

                var newVersion = db.version + 1;

                _deferReadiness(options);

                var dbContext = dbContexts[options.name];
                var forages = dbContext.forages;

                for (var i = 0; i < forages.length; i++) {
                    var forage = forages[i];
                    if (forage._dbInfo.db) {
                        forage._dbInfo.db.close();
                        forage._dbInfo.db = null;
                        forage._dbInfo.version = newVersion;
                    }
                }

                var dropObjectPromise = new Promise$1(function (resolve, reject) {
                    var req = idb.open(options.name, newVersion);

                    req.onerror = reject;

                    req.onupgradeneeded = function () {
                        var db = req.result;
                        db.deleteObjectStore(options.storeName);
                    };

                    req.onsuccess = function () {
                        var db = req.result;
                        resolve(db);
                    };
                });

                return dropObjectPromise.then(function (db) {
                    for (var j = 0; j < forages.length; j++) {
                        var forage = forages[j];
                        forage._dbInfo.db = db;
                        _advanceReadiness(forage._dbInfo);
                    }
                })["catch"](function (err) {
                    (_rejectReadiness(options, err) || Promise$1.resolve())["catch"](function () {});
                    throw err;
                });
            });
        }
    }

    executeCallback(promise, callback);
    return promise;
}

var asyncStorage = {
    _driver: 'asyncStorage',
    _initStorage: _initStorage,
    _support: isIndexedDBValid(),
    iterate: iterate,
    getItem: getItem,
    setItem: setItem,
    removeItem: removeItem,
    clear: clear,
    length: length,
    key: key,
    keys: keys,
    dropInstance: dropInstance
};

function isWebSQLValid() {
    return typeof openDatabase === 'function';
}

// Sadly, the best way to save binary data in WebSQL/localStorage is serializing
// it to Base64, so this is how we store it to prevent very strange errors with less
// verbose ways of binary <-> string data storage.
var BASE_CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

var BLOB_TYPE_PREFIX = '~~local_forage_type~';
var BLOB_TYPE_PREFIX_REGEX = /^~~local_forage_type~([^~]+)~/;

var SERIALIZED_MARKER = '__lfsc__:';
var SERIALIZED_MARKER_LENGTH = SERIALIZED_MARKER.length;

// OMG the serializations!
var TYPE_ARRAYBUFFER = 'arbf';
var TYPE_BLOB = 'blob';
var TYPE_INT8ARRAY = 'si08';
var TYPE_UINT8ARRAY = 'ui08';
var TYPE_UINT8CLAMPEDARRAY = 'uic8';
var TYPE_INT16ARRAY = 'si16';
var TYPE_INT32ARRAY = 'si32';
var TYPE_UINT16ARRAY = 'ur16';
var TYPE_UINT32ARRAY = 'ui32';
var TYPE_FLOAT32ARRAY = 'fl32';
var TYPE_FLOAT64ARRAY = 'fl64';
var TYPE_SERIALIZED_MARKER_LENGTH = SERIALIZED_MARKER_LENGTH + TYPE_ARRAYBUFFER.length;

var toString$1 = Object.prototype.toString;

function stringToBuffer(serializedString) {
    // Fill the string into a ArrayBuffer.
    var bufferLength = serializedString.length * 0.75;
    var len = serializedString.length;
    var i;
    var p = 0;
    var encoded1, encoded2, encoded3, encoded4;

    if (serializedString[serializedString.length - 1] === '=') {
        bufferLength--;
        if (serializedString[serializedString.length - 2] === '=') {
            bufferLength--;
        }
    }

    var buffer = new ArrayBuffer(bufferLength);
    var bytes = new Uint8Array(buffer);

    for (i = 0; i < len; i += 4) {
        encoded1 = BASE_CHARS.indexOf(serializedString[i]);
        encoded2 = BASE_CHARS.indexOf(serializedString[i + 1]);
        encoded3 = BASE_CHARS.indexOf(serializedString[i + 2]);
        encoded4 = BASE_CHARS.indexOf(serializedString[i + 3]);

        /*jslint bitwise: true */
        bytes[p++] = encoded1 << 2 | encoded2 >> 4;
        bytes[p++] = (encoded2 & 15) << 4 | encoded3 >> 2;
        bytes[p++] = (encoded3 & 3) << 6 | encoded4 & 63;
    }
    return buffer;
}

// Converts a buffer to a string to store, serialized, in the backend
// storage library.
function bufferToString(buffer) {
    // base64-arraybuffer
    var bytes = new Uint8Array(buffer);
    var base64String = '';
    var i;

    for (i = 0; i < bytes.length; i += 3) {
        /*jslint bitwise: true */
        base64String += BASE_CHARS[bytes[i] >> 2];
        base64String += BASE_CHARS[(bytes[i] & 3) << 4 | bytes[i + 1] >> 4];
        base64String += BASE_CHARS[(bytes[i + 1] & 15) << 2 | bytes[i + 2] >> 6];
        base64String += BASE_CHARS[bytes[i + 2] & 63];
    }

    if (bytes.length % 3 === 2) {
        base64String = base64String.substring(0, base64String.length - 1) + '=';
    } else if (bytes.length % 3 === 1) {
        base64String = base64String.substring(0, base64String.length - 2) + '==';
    }

    return base64String;
}

// Serialize a value, afterwards executing a callback (which usually
// instructs the `setItem()` callback/promise to be executed). This is how
// we store binary data with localStorage.
function serialize(value, callback) {
    var valueType = '';
    if (value) {
        valueType = toString$1.call(value);
    }

    // Cannot use `value instanceof ArrayBuffer` or such here, as these
    // checks fail when running the tests using casper.js...
    //
    // TODO: See why those tests fail and use a better solution.
    if (value && (valueType === '[object ArrayBuffer]' || value.buffer && toString$1.call(value.buffer) === '[object ArrayBuffer]')) {
        // Convert binary arrays to a string and prefix the string with
        // a special marker.
        var buffer;
        var marker = SERIALIZED_MARKER;

        if (value instanceof ArrayBuffer) {
            buffer = value;
            marker += TYPE_ARRAYBUFFER;
        } else {
            buffer = value.buffer;

            if (valueType === '[object Int8Array]') {
                marker += TYPE_INT8ARRAY;
            } else if (valueType === '[object Uint8Array]') {
                marker += TYPE_UINT8ARRAY;
            } else if (valueType === '[object Uint8ClampedArray]') {
                marker += TYPE_UINT8CLAMPEDARRAY;
            } else if (valueType === '[object Int16Array]') {
                marker += TYPE_INT16ARRAY;
            } else if (valueType === '[object Uint16Array]') {
                marker += TYPE_UINT16ARRAY;
            } else if (valueType === '[object Int32Array]') {
                marker += TYPE_INT32ARRAY;
            } else if (valueType === '[object Uint32Array]') {
                marker += TYPE_UINT32ARRAY;
            } else if (valueType === '[object Float32Array]') {
                marker += TYPE_FLOAT32ARRAY;
            } else if (valueType === '[object Float64Array]') {
                marker += TYPE_FLOAT64ARRAY;
            } else {
                callback(new Error('Failed to get type for BinaryArray'));
            }
        }

        callback(marker + bufferToString(buffer));
    } else if (valueType === '[object Blob]') {
        // Conver the blob to a binaryArray and then to a string.
        var fileReader = new FileReader();

        fileReader.onload = function () {
            // Backwards-compatible prefix for the blob type.
            var str = BLOB_TYPE_PREFIX + value.type + '~' + bufferToString(this.result);

            callback(SERIALIZED_MARKER + TYPE_BLOB + str);
        };

        fileReader.readAsArrayBuffer(value);
    } else {
        try {
            callback(JSON.stringify(value));
        } catch (e) {
            console.error("Couldn't convert value into a JSON string: ", value);

            callback(null, e);
        }
    }
}

// Deserialize data we've inserted into a value column/field. We place
// special markers into our strings to mark them as encoded; this isn't
// as nice as a meta field, but it's the only sane thing we can do whilst
// keeping localStorage support intact.
//
// Oftentimes this will just deserialize JSON content, but if we have a
// special marker (SERIALIZED_MARKER, defined above), we will extract
// some kind of arraybuffer/binary data/typed array out of the string.
function deserialize(value) {
    // If we haven't marked this string as being specially serialized (i.e.
    // something other than serialized JSON), we can just return it and be
    // done with it.
    if (value.substring(0, SERIALIZED_MARKER_LENGTH) !== SERIALIZED_MARKER) {
        return JSON.parse(value);
    }

    // The following code deals with deserializing some kind of Blob or
    // TypedArray. First we separate out the type of data we're dealing
    // with from the data itself.
    var serializedString = value.substring(TYPE_SERIALIZED_MARKER_LENGTH);
    var type = value.substring(SERIALIZED_MARKER_LENGTH, TYPE_SERIALIZED_MARKER_LENGTH);

    var blobType;
    // Backwards-compatible blob type serialization strategy.
    // DBs created with older versions of localForage will simply not have the blob type.
    if (type === TYPE_BLOB && BLOB_TYPE_PREFIX_REGEX.test(serializedString)) {
        var matcher = serializedString.match(BLOB_TYPE_PREFIX_REGEX);
        blobType = matcher[1];
        serializedString = serializedString.substring(matcher[0].length);
    }
    var buffer = stringToBuffer(serializedString);

    // Return the right type based on the code/type set during
    // serialization.
    switch (type) {
        case TYPE_ARRAYBUFFER:
            return buffer;
        case TYPE_BLOB:
            return createBlob([buffer], { type: blobType });
        case TYPE_INT8ARRAY:
            return new Int8Array(buffer);
        case TYPE_UINT8ARRAY:
            return new Uint8Array(buffer);
        case TYPE_UINT8CLAMPEDARRAY:
            return new Uint8ClampedArray(buffer);
        case TYPE_INT16ARRAY:
            return new Int16Array(buffer);
        case TYPE_UINT16ARRAY:
            return new Uint16Array(buffer);
        case TYPE_INT32ARRAY:
            return new Int32Array(buffer);
        case TYPE_UINT32ARRAY:
            return new Uint32Array(buffer);
        case TYPE_FLOAT32ARRAY:
            return new Float32Array(buffer);
        case TYPE_FLOAT64ARRAY:
            return new Float64Array(buffer);
        default:
            throw new Error('Unkown type: ' + type);
    }
}

var localforageSerializer = {
    serialize: serialize,
    deserialize: deserialize,
    stringToBuffer: stringToBuffer,
    bufferToString: bufferToString
};

/*
 * Includes code from:
 *
 * base64-arraybuffer
 * https://github.com/niklasvh/base64-arraybuffer
 *
 * Copyright (c) 2012 Niklas von Hertzen
 * Licensed under the MIT license.
 */

function createDbTable(t, dbInfo, callback, errorCallback) {
    t.executeSql('CREATE TABLE IF NOT EXISTS ' + dbInfo.storeName + ' ' + '(id INTEGER PRIMARY KEY, key unique, value)', [], callback, errorCallback);
}

// Open the WebSQL database (automatically creates one if one didn't
// previously exist), using any options set in the config.
function _initStorage$1(options) {
    var self = this;
    var dbInfo = {
        db: null
    };

    if (options) {
        for (var i in options) {
            dbInfo[i] = typeof options[i] !== 'string' ? options[i].toString() : options[i];
        }
    }

    var dbInfoPromise = new Promise$1(function (resolve, reject) {
        // Open the database; the openDatabase API will automatically
        // create it for us if it doesn't exist.
        try {
            dbInfo.db = openDatabase(dbInfo.name, String(dbInfo.version), dbInfo.description, dbInfo.size);
        } catch (e) {
            return reject(e);
        }

        // Create our key/value table if it doesn't exist.
        dbInfo.db.transaction(function (t) {
            createDbTable(t, dbInfo, function () {
                self._dbInfo = dbInfo;
                resolve();
            }, function (t, error) {
                reject(error);
            });
        }, reject);
    });

    dbInfo.serializer = localforageSerializer;
    return dbInfoPromise;
}

function tryExecuteSql(t, dbInfo, sqlStatement, args, callback, errorCallback) {
    t.executeSql(sqlStatement, args, callback, function (t, error) {
        if (error.code === error.SYNTAX_ERR) {
            t.executeSql('SELECT name FROM sqlite_master ' + "WHERE type='table' AND name = ?", [name], function (t, results) {
                if (!results.rows.length) {
                    // if the table is missing (was deleted)
                    // re-create it table and retry
                    createDbTable(t, dbInfo, function () {
                        t.executeSql(sqlStatement, args, callback, errorCallback);
                    }, errorCallback);
                } else {
                    errorCallback(t, error);
                }
            }, errorCallback);
        } else {
            errorCallback(t, error);
        }
    }, errorCallback);
}

function getItem$1(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'SELECT * FROM ' + dbInfo.storeName + ' WHERE key = ? LIMIT 1', [key], function (t, results) {
                    var result = results.rows.length ? results.rows.item(0).value : null;

                    // Check to see if this is serialized content we need to
                    // unpack.
                    if (result) {
                        result = dbInfo.serializer.deserialize(result);
                    }

                    resolve(result);
                }, function (t, error) {

                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function iterate$1(iterator, callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;

            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'SELECT * FROM ' + dbInfo.storeName, [], function (t, results) {
                    var rows = results.rows;
                    var length = rows.length;

                    for (var i = 0; i < length; i++) {
                        var item = rows.item(i);
                        var result = item.value;

                        // Check to see if this is serialized content
                        // we need to unpack.
                        if (result) {
                            result = dbInfo.serializer.deserialize(result);
                        }

                        result = iterator(result, item.key, i + 1);

                        // void(0) prevents problems with redefinition
                        // of `undefined`.
                        if (result !== void 0) {
                            resolve(result);
                            return;
                        }
                    }

                    resolve();
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function _setItem(key, value, callback, retriesLeft) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            // The localStorage API doesn't return undefined values in an
            // "expected" way, so undefined is always cast to null in all
            // drivers. See: https://github.com/mozilla/localForage/pull/42
            if (value === undefined) {
                value = null;
            }

            // Save the original value to pass to the callback.
            var originalValue = value;

            var dbInfo = self._dbInfo;
            dbInfo.serializer.serialize(value, function (value, error) {
                if (error) {
                    reject(error);
                } else {
                    dbInfo.db.transaction(function (t) {
                        tryExecuteSql(t, dbInfo, 'INSERT OR REPLACE INTO ' + dbInfo.storeName + ' ' + '(key, value) VALUES (?, ?)', [key, value], function () {
                            resolve(originalValue);
                        }, function (t, error) {
                            reject(error);
                        });
                    }, function (sqlError) {
                        // The transaction failed; check
                        // to see if it's a quota error.
                        if (sqlError.code === sqlError.QUOTA_ERR) {
                            // We reject the callback outright for now, but
                            // it's worth trying to re-run the transaction.
                            // Even if the user accepts the prompt to use
                            // more storage on Safari, this error will
                            // be called.
                            //
                            // Try to re-run the transaction.
                            if (retriesLeft > 0) {
                                resolve(_setItem.apply(self, [key, originalValue, callback, retriesLeft - 1]));
                                return;
                            }
                            reject(sqlError);
                        }
                    });
                }
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function setItem$1(key, value, callback) {
    return _setItem.apply(this, [key, value, callback, 1]);
}

function removeItem$1(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'DELETE FROM ' + dbInfo.storeName + ' WHERE key = ?', [key], function () {
                    resolve();
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

// Deletes every item in the table.
// TODO: Find out if this resets the AUTO_INCREMENT number.
function clear$1(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'DELETE FROM ' + dbInfo.storeName, [], function () {
                    resolve();
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

// Does a simple `COUNT(key)` to get the number of items stored in
// localForage.
function length$1(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                // Ahhh, SQL makes this one soooooo easy.
                tryExecuteSql(t, dbInfo, 'SELECT COUNT(key) as c FROM ' + dbInfo.storeName, [], function (t, results) {
                    var result = results.rows.item(0).c;
                    resolve(result);
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

// Return the key located at key index X; essentially gets the key from a
// `WHERE id = ?`. This is the most efficient way I can think to implement
// this rarely-used (in my experience) part of the API, but it can seem
// inconsistent, because we do `INSERT OR REPLACE INTO` on `setItem()`, so
// the ID of each key will change every time it's updated. Perhaps a stored
// procedure for the `setItem()` SQL would solve this problem?
// TODO: Don't change ID on `setItem()`.
function key$1(n, callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'SELECT key FROM ' + dbInfo.storeName + ' WHERE id = ? LIMIT 1', [n + 1], function (t, results) {
                    var result = results.rows.length ? results.rows.item(0).key : null;
                    resolve(result);
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

function keys$1(callback) {
    var self = this;

    var promise = new Promise$1(function (resolve, reject) {
        self.ready().then(function () {
            var dbInfo = self._dbInfo;
            dbInfo.db.transaction(function (t) {
                tryExecuteSql(t, dbInfo, 'SELECT key FROM ' + dbInfo.storeName, [], function (t, results) {
                    var keys = [];

                    for (var i = 0; i < results.rows.length; i++) {
                        keys.push(results.rows.item(i).key);
                    }

                    resolve(keys);
                }, function (t, error) {
                    reject(error);
                });
            });
        })["catch"](reject);
    });

    executeCallback(promise, callback);
    return promise;
}

// https://www.w3.org/TR/webdatabase/#databases
// > There is no way to enumerate or delete the databases available for an origin from this API.
function getAllStoreNames(db) {
    return new Promise$1(function (resolve, reject) {
        db.transaction(function (t) {
            t.executeSql('SELECT name FROM sqlite_master ' + "WHERE type='table' AND name <> '__WebKitDatabaseInfoTable__'", [], function (t, results) {
                var storeNames = [];

                for (var i = 0; i < results.rows.length; i++) {
                    storeNames.push(results.rows.item(i).name);
                }

                resolve({
                    db: db,
                    storeNames: storeNames
                });
            }, function (t, error) {
                reject(error);
            });
        }, function (sqlError) {
            reject(sqlError);
        });
    });
}

function dropInstance$1(options, callback) {
    callback = getCallback.apply(this, arguments);

    var currentConfig = this.config();
    options = typeof options !== 'function' && options || {};
    if (!options.name) {
        options.name = options.name || currentConfig.name;
        options.storeName = options.storeName || currentConfig.storeName;
    }

    var self = this;
    var promise;
    if (!options.name) {
        promise = Promise$1.reject('Invalid arguments');
    } else {
        promise = new Promise$1(function (resolve) {
            var db;
            if (options.name === currentConfig.name) {
                // use the db reference of the current instance
                db = self._dbInfo.db;
            } else {
                db = openDatabase(options.name, '', '', 0);
            }

            if (!options.storeName) {
                // drop all database tables
                resolve(getAllStoreNames(db));
            } else {
                resolve({
                    db: db,
                    storeNames: [options.storeName]
                });
            }
        }).then(function (operationInfo) {
            return new Promise$1(function (resolve, reject) {
                operationInfo.db.transaction(function (t) {
                    function dropTable(storeName) {
                        return new Promise$1(function (resolve, reject) {
                            t.executeSql('DROP TABLE IF EXISTS ' + storeName, [], function () {
                                resolve();
                            }, function (t, error) {
                                reject(error);
                            });
                        });
                    }

                    var operations = [];
                    for (var i = 0, len = operationInfo.storeNames.length; i < len; i++) {
                        operations.push(dropTable(operationInfo.storeNames[i]));
                    }

                    Promise$1.all(operations).then(function () {
                        resolve();
                    })["catch"](function (e) {
                        reject(e);
                    });
                }, function (sqlError) {
                    reject(sqlError);
                });
            });
        });
    }

    executeCallback(promise, callback);
    return promise;
}

var webSQLStorage = {
    _driver: 'webSQLStorage',
    _initStorage: _initStorage$1,
    _support: isWebSQLValid(),
    iterate: iterate$1,
    getItem: getItem$1,
    setItem: setItem$1,
    removeItem: removeItem$1,
    clear: clear$1,
    length: length$1,
    key: key$1,
    keys: keys$1,
    dropInstance: dropInstance$1
};

function isLocalStorageValid() {
    try {
        return typeof localStorage !== 'undefined' && 'setItem' in localStorage && typeof localStorage.setItem === 'function';
    } catch (e) {
        return false;
    }
}

function _getKeyPrefix(options, defaultConfig) {
    var keyPrefix = options.name + '/';

    if (options.storeName !== defaultConfig.storeName) {
        keyPrefix += options.storeName + '/';
    }
    return keyPrefix;
}

// Check if localStorage throws when saving an item
function checkIfLocalStorageThrows() {
    var localStorageTestKey = '_localforage_support_test';

    try {
        localStorage.setItem(localStorageTestKey, true);
        localStorage.removeItem(localStorageTestKey);

        return false;
    } catch (e) {
        return true;
    }
}

// Check if localStorage is usable and allows to save an item
// This method checks if localStorage is usable in Safari Private Browsing
// mode, or in any other case where the available quota for localStorage
// is 0 and there wasn't any saved items yet.
function _isLocalStorageUsable() {
    return !checkIfLocalStorageThrows() || localStorage.length > 0;
}

// Config the localStorage backend, using options set in the config.
function _initStorage$2(options) {
    var self = this;
    var dbInfo = {};
    if (options) {
        for (var i in options) {
            dbInfo[i] = options[i];
        }
    }

    dbInfo.keyPrefix = _getKeyPrefix(options, self._defaultConfig);

    if (!_isLocalStorageUsable()) {
        return Promise$1.reject();
    }

    self._dbInfo = dbInfo;
    dbInfo.serializer = localforageSerializer;

    return Promise$1.resolve();
}

// Remove all keys from the datastore, effectively destroying all data in
// the app's key/value store!
function clear$2(callback) {
    var self = this;
    var promise = self.ready().then(function () {
        var keyPrefix = self._dbInfo.keyPrefix;

        for (var i = localStorage.length - 1; i >= 0; i--) {
            var key = localStorage.key(i);

            if (key.indexOf(keyPrefix) === 0) {
                localStorage.removeItem(key);
            }
        }
    });

    executeCallback(promise, callback);
    return promise;
}

// Retrieve an item from the store. Unlike the original async_storage
// library in Gaia, we don't modify return values at all. If a key's value
// is `undefined`, we pass that value to the callback function.
function getItem$2(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = self.ready().then(function () {
        var dbInfo = self._dbInfo;
        var result = localStorage.getItem(dbInfo.keyPrefix + key);

        // If a result was found, parse it from the serialized
        // string into a JS object. If result isn't truthy, the key
        // is likely undefined and we'll pass it straight to the
        // callback.
        if (result) {
            result = dbInfo.serializer.deserialize(result);
        }

        return result;
    });

    executeCallback(promise, callback);
    return promise;
}

// Iterate over all items in the store.
function iterate$2(iterator, callback) {
    var self = this;

    var promise = self.ready().then(function () {
        var dbInfo = self._dbInfo;
        var keyPrefix = dbInfo.keyPrefix;
        var keyPrefixLength = keyPrefix.length;
        var length = localStorage.length;

        // We use a dedicated iterator instead of the `i` variable below
        // so other keys we fetch in localStorage aren't counted in
        // the `iterationNumber` argument passed to the `iterate()`
        // callback.
        //
        // See: github.com/mozilla/localForage/pull/435#discussion_r38061530
        var iterationNumber = 1;

        for (var i = 0; i < length; i++) {
            var key = localStorage.key(i);
            if (key.indexOf(keyPrefix) !== 0) {
                continue;
            }
            var value = localStorage.getItem(key);

            // If a result was found, parse it from the serialized
            // string into a JS object. If result isn't truthy, the
            // key is likely undefined and we'll pass it straight
            // to the iterator.
            if (value) {
                value = dbInfo.serializer.deserialize(value);
            }

            value = iterator(value, key.substring(keyPrefixLength), iterationNumber++);

            if (value !== void 0) {
                return value;
            }
        }
    });

    executeCallback(promise, callback);
    return promise;
}

// Same as localStorage's key() method, except takes a callback.
function key$2(n, callback) {
    var self = this;
    var promise = self.ready().then(function () {
        var dbInfo = self._dbInfo;
        var result;
        try {
            result = localStorage.key(n);
        } catch (error) {
            result = null;
        }

        // Remove the prefix from the key, if a key is found.
        if (result) {
            result = result.substring(dbInfo.keyPrefix.length);
        }

        return result;
    });

    executeCallback(promise, callback);
    return promise;
}

function keys$2(callback) {
    var self = this;
    var promise = self.ready().then(function () {
        var dbInfo = self._dbInfo;
        var length = localStorage.length;
        var keys = [];

        for (var i = 0; i < length; i++) {
            var itemKey = localStorage.key(i);
            if (itemKey.indexOf(dbInfo.keyPrefix) === 0) {
                keys.push(itemKey.substring(dbInfo.keyPrefix.length));
            }
        }

        return keys;
    });

    executeCallback(promise, callback);
    return promise;
}

// Supply the number of keys in the datastore to the callback function.
function length$2(callback) {
    var self = this;
    var promise = self.keys().then(function (keys) {
        return keys.length;
    });

    executeCallback(promise, callback);
    return promise;
}

// Remove an item from the store, nice and simple.
function removeItem$2(key, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = self.ready().then(function () {
        var dbInfo = self._dbInfo;
        localStorage.removeItem(dbInfo.keyPrefix + key);
    });

    executeCallback(promise, callback);
    return promise;
}

// Set a key's value and run an optional callback once the value is set.
// Unlike Gaia's implementation, the callback function is passed the value,
// in case you want to operate on that value only after you're sure it
// saved, or something like that.
function setItem$2(key, value, callback) {
    var self = this;

    key = normalizeKey(key);

    var promise = self.ready().then(function () {
        // Convert undefined values to null.
        // https://github.com/mozilla/localForage/pull/42
        if (value === undefined) {
            value = null;
        }

        // Save the original value to pass to the callback.
        var originalValue = value;

        return new Promise$1(function (resolve, reject) {
            var dbInfo = self._dbInfo;
            dbInfo.serializer.serialize(value, function (value, error) {
                if (error) {
                    reject(error);
                } else {
                    try {
                        localStorage.setItem(dbInfo.keyPrefix + key, value);
                        resolve(originalValue);
                    } catch (e) {
                        // localStorage capacity exceeded.
                        // TODO: Make this a specific error/event.
                        if (e.name === 'QuotaExceededError' || e.name === 'NS_ERROR_DOM_QUOTA_REACHED') {
                            reject(e);
                        }
                        reject(e);
                    }
                }
            });
        });
    });

    executeCallback(promise, callback);
    return promise;
}

function dropInstance$2(options, callback) {
    callback = getCallback.apply(this, arguments);

    options = typeof options !== 'function' && options || {};
    if (!options.name) {
        var currentConfig = this.config();
        options.name = options.name || currentConfig.name;
        options.storeName = options.storeName || currentConfig.storeName;
    }

    var self = this;
    var promise;
    if (!options.name) {
        promise = Promise$1.reject('Invalid arguments');
    } else {
        promise = new Promise$1(function (resolve) {
            if (!options.storeName) {
                resolve(options.name + '/');
            } else {
                resolve(_getKeyPrefix(options, self._defaultConfig));
            }
        }).then(function (keyPrefix) {
            for (var i = localStorage.length - 1; i >= 0; i--) {
                var key = localStorage.key(i);

                if (key.indexOf(keyPrefix) === 0) {
                    localStorage.removeItem(key);
                }
            }
        });
    }

    executeCallback(promise, callback);
    return promise;
}

var localStorageWrapper = {
    _driver: 'localStorageWrapper',
    _initStorage: _initStorage$2,
    _support: isLocalStorageValid(),
    iterate: iterate$2,
    getItem: getItem$2,
    setItem: setItem$2,
    removeItem: removeItem$2,
    clear: clear$2,
    length: length$2,
    key: key$2,
    keys: keys$2,
    dropInstance: dropInstance$2
};

var isArray = Array.isArray || function (arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
};

// Drivers are stored here when `defineDriver()` is called.
// They are shared across all instances of localForage.
var DefinedDrivers = {};

var DriverSupport = {};

var DefaultDrivers = {
    INDEXEDDB: asyncStorage,
    WEBSQL: webSQLStorage,
    LOCALSTORAGE: localStorageWrapper
};

var DefaultDriverOrder = [DefaultDrivers.INDEXEDDB._driver, DefaultDrivers.WEBSQL._driver, DefaultDrivers.LOCALSTORAGE._driver];

var OptionalDriverMethods = ['dropInstance'];

var LibraryMethods = ['clear', 'getItem', 'iterate', 'key', 'keys', 'length', 'removeItem', 'setItem'].concat(OptionalDriverMethods);

var DefaultConfig = {
    description: '',
    driver: DefaultDriverOrder.slice(),
    name: 'localforage',
    // Default DB size is _JUST UNDER_ 5MB, as it's the highest size
    // we can use without a prompt.
    size: 4980736,
    storeName: 'keyvaluepairs',
    version: 1.0
};

function callWhenReady(localForageInstance, libraryMethod) {
    localForageInstance[libraryMethod] = function () {
        var _args = arguments;
        return localForageInstance.ready().then(function () {
            return localForageInstance[libraryMethod].apply(localForageInstance, _args);
        });
    };
}

function extend() {
    for (var i = 1; i < arguments.length; i++) {
        var arg = arguments[i];

        if (arg) {
            for (var _key in arg) {
                if (arg.hasOwnProperty(_key)) {
                    if (isArray(arg[_key])) {
                        arguments[0][_key] = arg[_key].slice();
                    } else {
                        arguments[0][_key] = arg[_key];
                    }
                }
            }
        }
    }

    return arguments[0];
}

var LocalForage = function () {
    function LocalForage(options) {
        _classCallCheck(this, LocalForage);

        for (var driverTypeKey in DefaultDrivers) {
            if (DefaultDrivers.hasOwnProperty(driverTypeKey)) {
                var driver = DefaultDrivers[driverTypeKey];
                var driverName = driver._driver;
                this[driverTypeKey] = driverName;

                if (!DefinedDrivers[driverName]) {
                    // we don't need to wait for the promise,
                    // since the default drivers can be defined
                    // in a blocking manner
                    this.defineDriver(driver);
                }
            }
        }

        this._defaultConfig = extend({}, DefaultConfig);
        this._config = extend({}, this._defaultConfig, options);
        this._driverSet = null;
        this._initDriver = null;
        this._ready = false;
        this._dbInfo = null;

        this._wrapLibraryMethodsWithReady();
        this.setDriver(this._config.driver)["catch"](function () {});
    }

    // Set any config values for localForage; can be called anytime before
    // the first API call (e.g. `getItem`, `setItem`).
    // We loop through options so we don't overwrite existing config
    // values.


    LocalForage.prototype.config = function config(options) {
        // If the options argument is an object, we use it to set values.
        // Otherwise, we return either a specified config value or all
        // config values.
        if ((typeof options === 'undefined' ? 'undefined' : _typeof(options)) === 'object') {
            // If localforage is ready and fully initialized, we can't set
            // any new configuration values. Instead, we return an error.
            if (this._ready) {
                return new Error('Can\'t call config() after localforage ' + 'has been used.');
            }

            for (var i in options) {
                if (i === 'storeName') {
                    options[i] = options[i].replace(/\W/g, '_');
                }

                if (i === 'version' && typeof options[i] !== 'number') {
                    return new Error('Database version must be a number.');
                }

                this._config[i] = options[i];
            }

            // after all config options are set and
            // the driver option is used, try setting it
            if ('driver' in options && options.driver) {
                return this.setDriver(this._config.driver);
            }

            return true;
        } else if (typeof options === 'string') {
            return this._config[options];
        } else {
            return this._config;
        }
    };

    // Used to define a custom driver, shared across all instances of
    // localForage.


    LocalForage.prototype.defineDriver = function defineDriver(driverObject, callback, errorCallback) {
        var promise = new Promise$1(function (resolve, reject) {
            try {
                var driverName = driverObject._driver;
                var complianceError = new Error('Custom driver not compliant; see ' + 'https://mozilla.github.io/localForage/#definedriver');

                // A driver name should be defined and not overlap with the
                // library-defined, default drivers.
                if (!driverObject._driver) {
                    reject(complianceError);
                    return;
                }

                var driverMethods = LibraryMethods.concat('_initStorage');
                for (var i = 0, len = driverMethods.length; i < len; i++) {
                    var driverMethodName = driverMethods[i];

                    // when the property is there,
                    // it should be a method even when optional
                    var isRequired = OptionalDriverMethods.indexOf(driverMethodName) < 0;
                    if ((isRequired || driverObject[driverMethodName]) && typeof driverObject[driverMethodName] !== 'function') {
                        reject(complianceError);
                        return;
                    }
                }

                var configureMissingMethods = function configureMissingMethods() {
                    var methodNotImplementedFactory = function methodNotImplementedFactory(methodName) {
                        return function () {
                            var error = new Error('Method ' + methodName + ' is not implemented by the current driver');
                            var promise = Promise$1.reject(error);
                            executeCallback(promise, arguments[arguments.length - 1]);
                            return promise;
                        };
                    };

                    for (var _i = 0, _len = OptionalDriverMethods.length; _i < _len; _i++) {
                        var optionalDriverMethod = OptionalDriverMethods[_i];
                        if (!driverObject[optionalDriverMethod]) {
                            driverObject[optionalDriverMethod] = methodNotImplementedFactory(optionalDriverMethod);
                        }
                    }
                };

                configureMissingMethods();

                var setDriverSupport = function setDriverSupport(support) {
                    if (DefinedDrivers[driverName]) {
                        console.info('Redefining LocalForage driver: ' + driverName);
                    }
                    DefinedDrivers[driverName] = driverObject;
                    DriverSupport[driverName] = support;
                    // don't use a then, so that we can define
                    // drivers that have simple _support methods
                    // in a blocking manner
                    resolve();
                };

                if ('_support' in driverObject) {
                    if (driverObject._support && typeof driverObject._support === 'function') {
                        driverObject._support().then(setDriverSupport, reject);
                    } else {
                        setDriverSupport(!!driverObject._support);
                    }
                } else {
                    setDriverSupport(true);
                }
            } catch (e) {
                reject(e);
            }
        });

        executeTwoCallbacks(promise, callback, errorCallback);
        return promise;
    };

    LocalForage.prototype.driver = function driver() {
        return this._driver || null;
    };

    LocalForage.prototype.getDriver = function getDriver(driverName, callback, errorCallback) {
        var getDriverPromise = DefinedDrivers[driverName] ? Promise$1.resolve(DefinedDrivers[driverName]) : Promise$1.reject(new Error('Driver not found.'));

        executeTwoCallbacks(getDriverPromise, callback, errorCallback);
        return getDriverPromise;
    };

    LocalForage.prototype.getSerializer = function getSerializer(callback) {
        var serializerPromise = Promise$1.resolve(localforageSerializer);
        executeTwoCallbacks(serializerPromise, callback);
        return serializerPromise;
    };

    LocalForage.prototype.ready = function ready(callback) {
        var self = this;

        var promise = self._driverSet.then(function () {
            if (self._ready === null) {
                self._ready = self._initDriver();
            }

            return self._ready;
        });

        executeTwoCallbacks(promise, callback, callback);
        return promise;
    };

    LocalForage.prototype.setDriver = function setDriver(drivers, callback, errorCallback) {
        var self = this;

        if (!isArray(drivers)) {
            drivers = [drivers];
        }

        var supportedDrivers = this._getSupportedDrivers(drivers);

        function setDriverToConfig() {
            self._config.driver = self.driver();
        }

        function extendSelfWithDriver(driver) {
            self._extend(driver);
            setDriverToConfig();

            self._ready = self._initStorage(self._config);
            return self._ready;
        }

        function initDriver(supportedDrivers) {
            return function () {
                var currentDriverIndex = 0;

                function driverPromiseLoop() {
                    while (currentDriverIndex < supportedDrivers.length) {
                        var driverName = supportedDrivers[currentDriverIndex];
                        currentDriverIndex++;

                        self._dbInfo = null;
                        self._ready = null;

                        return self.getDriver(driverName).then(extendSelfWithDriver)["catch"](driverPromiseLoop);
                    }

                    setDriverToConfig();
                    var error = new Error('No available storage method found.');
                    self._driverSet = Promise$1.reject(error);
                    return self._driverSet;
                }

                return driverPromiseLoop();
            };
        }

        // There might be a driver initialization in progress
        // so wait for it to finish in order to avoid a possible
        // race condition to set _dbInfo
        var oldDriverSetDone = this._driverSet !== null ? this._driverSet["catch"](function () {
            return Promise$1.resolve();
        }) : Promise$1.resolve();

        this._driverSet = oldDriverSetDone.then(function () {
            var driverName = supportedDrivers[0];
            self._dbInfo = null;
            self._ready = null;

            return self.getDriver(driverName).then(function (driver) {
                self._driver = driver._driver;
                setDriverToConfig();
                self._wrapLibraryMethodsWithReady();
                self._initDriver = initDriver(supportedDrivers);
            });
        })["catch"](function () {
            setDriverToConfig();
            var error = new Error('No available storage method found.');
            self._driverSet = Promise$1.reject(error);
            return self._driverSet;
        });

        executeTwoCallbacks(this._driverSet, callback, errorCallback);
        return this._driverSet;
    };

    LocalForage.prototype.supports = function supports(driverName) {
        return !!DriverSupport[driverName];
    };

    LocalForage.prototype._extend = function _extend(libraryMethodsAndProperties) {
        extend(this, libraryMethodsAndProperties);
    };

    LocalForage.prototype._getSupportedDrivers = function _getSupportedDrivers(drivers) {
        var supportedDrivers = [];
        for (var i = 0, len = drivers.length; i < len; i++) {
            var driverName = drivers[i];
            if (this.supports(driverName)) {
                supportedDrivers.push(driverName);
            }
        }
        return supportedDrivers;
    };

    LocalForage.prototype._wrapLibraryMethodsWithReady = function _wrapLibraryMethodsWithReady() {
        // Add a stub for each driver API method that delays the call to the
        // corresponding driver method until localForage is ready. These stubs
        // will be replaced by the driver methods as soon as the driver is
        // loaded, so there is no performance impact.
        for (var i = 0, len = LibraryMethods.length; i < len; i++) {
            callWhenReady(this, LibraryMethods[i]);
        }
    };

    LocalForage.prototype.createInstance = function createInstance(options) {
        return new LocalForage(options);
    };

    return LocalForage;
}();

// The actual localForage object that we expose as a module or via a
// global. It's extended by pulling in one of our other libraries.


var localforage_js = new LocalForage();

module.exports = localforage_js;

},{"undefined":undefined}]},{},[1])(1)
});