@wry/context/lib/slot.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.Slot = void 0;
// This currentContext variable will only be used if the makeSlotClass
// function is called, which happens only if this is the first copy of the
// @wry/context package to be imported.
var currentContext = null;
// This unique internal object is used to denote the absence of a value
// for a given Slot, and is never exposed to outside code.
var MISSING_VALUE = {};
var idCounter = 1;
// Although we can't do anything about the cost of duplicated code from
// accidentally bundling multiple copies of the @wry/context package, we can
// avoid creating the Slot class more than once using makeSlotClass.
var makeSlotClass = function () { return /** @class */ (function () {
    function Slot() {
        // If you have a Slot object, you can find out its slot.id, but you cannot
        // guess the slot.id of a Slot you don't have access to, thanks to the
        // randomized suffix.
        this.id = [
            "slot",
            idCounter++,
            Date.now(),
            Math.random().toString(36).slice(2),
        ].join(":");
    }
    Slot.prototype.hasValue = function () {
        for (var context_1 = currentContext; context_1; context_1 = context_1.parent) {
            // We use the Slot object iself as a key to its value, which means the
            // value cannot be obtained without a reference to the Slot object.
            if (this.id in context_1.slots) {
                var value = context_1.slots[this.id];
                if (value === MISSING_VALUE)
                    break;
                if (context_1 !== currentContext) {
                    // Cache the value in currentContext.slots so the next lookup will
                    // be faster. This caching is safe because the tree of contexts and
                    // the values of the slots are logically immutable.
                    currentContext.slots[this.id] = value;
                }
                return true;
            }
        }
        if (currentContext) {
            // If a value was not found for this Slot, it's never going to be found
            // no matter how many times we look it up, so we might as well cache
            // the absence of the value, too.
            currentContext.slots[this.id] = MISSING_VALUE;
        }
        return false;
    };
    Slot.prototype.getValue = function () {
        if (this.hasValue()) {
            return currentContext.slots[this.id];
        }
    };
    Slot.prototype.withValue = function (value, callback, 
    // Given the prevalence of arrow functions, specifying arguments is likely
    // to be much more common than specifying `this`, hence this ordering:
    args, thisArg) {
        var _a;
        var slots = (_a = {
                __proto__: null
            },
            _a[this.id] = value,
            _a);
        var parent = currentContext;
        currentContext = { parent: parent, slots: slots };
        try {
            // Function.prototype.apply allows the arguments array argument to be
            // omitted or undefined, so args! is fine here.
            return callback.apply(thisArg, args);
        }
        finally {
            currentContext = parent;
        }
    };
    // Capture the current context and wrap a callback function so that it
    // reestablishes the captured context when called.
    Slot.bind = function (callback) {
        var context = currentContext;
        return function () {
            var saved = currentContext;
            try {
                currentContext = context;
                return callback.apply(this, arguments);
            }
            finally {
                currentContext = saved;
            }
        };
    };
    // Immediately run a callback function without any captured context.
    Slot.noContext = function (callback, 
    // Given the prevalence of arrow functions, specifying arguments is likely
    // to be much more common than specifying `this`, hence this ordering:
    args, thisArg) {
        if (currentContext) {
            var saved = currentContext;
            try {
                currentContext = null;
                // Function.prototype.apply allows the arguments array argument to be
                // omitted or undefined, so args! is fine here.
                return callback.apply(thisArg, args);
            }
            finally {
                currentContext = saved;
            }
        }
        else {
            return callback.apply(thisArg, args);
        }
    };
    return Slot;
}()); };
function maybe(fn) {
    try {
        return fn();
    }
    catch (ignored) { }
}
// We store a single global implementation of the Slot class as a permanent
// non-enumerable property of the globalThis object. This obfuscation does
// nothing to prevent access to the Slot class, but at least it ensures the
// implementation (i.e. currentContext) cannot be tampered with, and all copies
// of the @wry/context package (hopefully just one) will share the same Slot
// implementation. Since the first copy of the @wry/context package to be
// imported wins, this technique imposes a steep cost for any future breaking
// changes to the Slot class.
var globalKey = "@wry/context:Slot";
var host = 
// Prefer globalThis when available.
// https://github.com/benjamn/wryware/issues/347
maybe(function () { return globalThis; }) ||
    // Fall back to global, which works in Node.js and may be converted by some
    // bundlers to the appropriate identifier (window, self, ...) depending on the
    // bundling target. https://github.com/endojs/endo/issues/576#issuecomment-1178515224
    maybe(function () { return global; }) ||
    // Otherwise, use a dummy host that's local to this module. We used to fall
    // back to using the Array constructor as a namespace, but that was flagged in
    // https://github.com/benjamn/wryware/issues/347, and can be avoided.
    Object.create(null);
// Whichever globalHost we're using, make TypeScript happy about the additional
// globalKey property.
var globalHost = host;
exports.Slot = globalHost[globalKey] ||
    // Earlier versions of this package stored the globalKey property on the Array
    // constructor, so we check there as well, to prevent Slot class duplication.
    Array[globalKey] ||
    (function (Slot) {
        try {
            Object.defineProperty(globalHost, globalKey, {
                value: Slot,
                enumerable: false,
                writable: false,
                // When it was possible for globalHost to be the Array constructor (a
                // legacy Slot dedup strategy), it was important for the property to be
                // configurable:true so it could be deleted. That does not seem to be as
                // important when globalHost is the global object, but I don't want to
                // cause similar problems again, and configurable:true seems safest.
                // https://github.com/endojs/endo/issues/576#issuecomment-1178274008
                configurable: true
            });
        }
        finally {
            return Slot;
        }
    })(makeSlotClass());
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