# BrowserFS v0.6.0
> BrowserFS is an in-browser file system that emulates the [Node JS file system API](http://nodejs.org/api/fs.html) and supports storing and retrieving files from various backends. BrowserFS also integrates nicely into the Emscripten file system.

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### Backends

BrowserFS is highly extensible, and ships with many filesystem backends:

* `XmlHttpRequest`: Downloads files on-demand from a webserver via `XMLHttpRequest`
* `LocalStorage`: Stores files in the browser's `localStorage`.
* `HTML5FS`: Stores files into the HTML5 `FileSystem` API
* `IndexedDB`: Stores files into the browser's `IndexedDB` object database.
* `Dropbox`: Stores files into the user's Dropbox account.
  * Note: You provide this filesystem with an authenticated [DropboxJS client](https://github.com/dropbox/dropbox-js)
* `InMemory`: Stores files in-memory. Thus, it is a temporary file store that clears when the user navigates away.
* `ZipFS`: Read-only zip file-backed FS. Lazily decompresses files as you access them.
* `WorkerFS`: Lets you mount the BrowserFS file system configured in the main thread in a WebWorker, or the other way around!
* `MountableFileSystem`: Lets you mount multiple file systems into a single directory hierarchy, as in *nix-based OSes.
* `OverlayFS`: Mount a read-only file system as read-write by overlaying a writable file system on top of it. Like Docker's overlayfs, it will only write changed files to the writable file system.
* `AsyncMirrorFS`: Use an asynchronous backend synchronously. Invaluable for Emscripten; let your Emscripten applications write to larger file stores with no additional effort!
  * Note: Loads the entire contents of the file system into a synchronous backend during construction. Performs synchronous operations in-memory, and enqueues them to be mirrored onto the asynchronous backend.
* `FolderAdapter`: Wraps a file system, and scopes all interactions to a subfolder of that file system.
* `Emscripten`: Lets you mount Emscripten file systems inside BrowserFS.

More backends can be defined by separate libraries, so long as they extend the `BaseFileSystem`. Multiple backends can be active at once at different locations in the directory hierarchy.

For more information, see the [wiki](https://github.com/jvilk/BrowserFS/wiki).

### Building

Prerequisites:

* Node and NPM
* Grunt-cli globally installed: `npm install -g grunt-cli`
* Run `npm install` to install local dependencies

Release:

    grunt

The minified release build can be found in `build/browserfs.min.js`.

Development:

    grunt dev

The development build can be found as `build/browserfs.js`.

Custom builds:

If you want to build BrowserFS with a subset of the available backends,
change the `getBackends()` function in `Gruntfile.js` to return an
array of backends you wish to use. Then, perform a release build.

### Using
Here's a simple example, using the LocalStorage-backed file system:

```html
<script type="text/javascript" src="browserfs.min.js"></script>
<script type="text/javascript">
  // Installs globals onto window:
  // * Buffer
  // * require (monkey-patches if already defined)
  // * process
  // You can pass in an arbitrary object if you do not wish to pollute
  // the global namespace.
  BrowserFS.install(window);
  // Constructs an instance of the LocalStorage-backed file system.
  var lsfs = new BrowserFS.FileSystem.LocalStorage();
  // Initialize it as the root file system.
  BrowserFS.initialize(lsfs);
</script>
```

Now, you can write code like this:

```js
var fs = require('fs');
fs.writeFile('/test.txt', 'Cool, I can do this in the browser!', function(err) {
  fs.readFile('/test.txt', function(err, contents) {
    console.log(contents.toString());
  });
});
```

### Using with Browserify

You can use BrowserFS with your Browserify projects. Simply depend on `browserfs/dist/node/core/node_fs.js` as the provider
of `fs`, and pull in `browserfs/dist/node/main.js` as the provider of the `BrowserFS` variable, through which you
can construct and initialize the file system.

Do not depend on both `node_fs.js` and the `browserfs` module, as it will pull in the node modules from `dist/node`,
as well as `dist/browserfs.js`.

Optionally, you can also use the companion modules `bfs-path`, `bfs-buffer`, and `bfs-process` to replace
browserify's builtins for `path`, `buffer`, and `process`.

I have written an [example project](https://github.com/jvilk/bfs-browserify-test) that illustrates how to do this.

### Using with Node

You can use BrowserFS with Node. Simply add `browserfs` as an NPM dependency, and `require('browserfs')`.
The object returned from this action is the same `BrowserFS` global described above.

If you need BrowserFS to return Node Buffer objects (instead of objects that implement the same interface),
simply `require('browserfs/dist/node/main')` instead.

### Using with Emscripten

You can use any *synchronous* BrowserFS file systems with Emscripten!
Persist particular folders in the Emscripten file system to `localStorage`, or enable Emscripten to synchronously download files from another folder as they are requested.

Include `browserfs.min.js` into the page, and add code similar to the following to your `Module`'s `preRun` array:

```javascript
/**
 * Mounts a localStorage-backed file system into the /data folder of Emscripten's file system.
 */
function setupBFS() {
  // Constructs an instance of the LocalStorage-backed file system.
  var lsfs = new BrowserFS.FileSystem.LocalStorage();
  // Initialize it as the root file system.
  BrowserFS.initialize(lsfs);
  // Grab the BrowserFS Emscripten FS plugin.
  var BFS = new BrowserFS.EmscriptenFS();
  // Create the folder that we'll turn into a mount point.
  FS.createFolder(FS.root, 'data', true, true);
  // Mount BFS's root folder into the '/data' folder.
  FS.mount(BFS, {root: '/'}, '/data');
}
```

Note: Do **NOT** use `BrowserFS.install(window)` on a page with an Emscripten application! Emscripten will be tricked into thinking that it is running in Node JS.

If you wish to use an asynchronous BrowserFS backend with Emscripten (e.g. Dropbox), you'll need to wrap it into an `AsyncMirror` file system first:

```javascript
/**
 * Run this prior to starting your Emscripten module.
 * @param dropboxClient An authenticated DropboxJS client.
 */
function asyncSetup(dropboxClient, cb) {
  var dbfs = new BrowserFS.FileSystem.Dropbox(dropboxClient);
  // Wrap in AsyncMirrorFS.
  var asyncMirror = new BrowserFS.FileSystem.AsyncMirror(
    new BrowserFS.FileSystem.InMemory(), dbfs);

  // Downloads the entire contents of the Dropbox backend into memory.
  // You'll probably want to use an app folder, and check that you
  // aren't pulling in a huge amount of data here.
  asyncMirror.initialize(function(err) {
    // Initialize it as the root file system.
    BrowserFS.initialize(asyncMirror);
    // BFS is ready for Emscripten!
    cb();
  });
}
function setupBFS() {
  // Grab the BrowserFS Emscripten FS plugin.
  var BFS = new BrowserFS.EmscriptenFS();
  // Create the folder that we'll turn into a mount point.
  FS.createFolder(FS.root, 'data', true, true);
  // Mount BFS's root folder into the '/data' folder.
  FS.mount(BFS, {root: '/'}, '/data');
}
```

### Testing

To run unit tests, simply run `grunt test`.

`grunt coverage` will run the unit tests, and output code coverage information.

### License

BrowserFS is licensed under the MIT License. See `LICENSE` for details.