Source: d:/wamp/www/phaser/src/pixi/loaders/AssetLoader.js

/**
 * @author Mat Groves http://matgroves.com/ @Doormat23
 */

/**
 * A Class that loads a bunch of images / sprite sheet / bitmap font files. Once the
 * assets have been loaded they are added to the PIXI Texture cache and can be accessed
 * easily through PIXI.Texture.fromImage() and PIXI.Sprite.fromImage()
 * When all items have been loaded this class will dispatch a 'onLoaded' event
 * As each individual item is loaded this class will dispatch a 'onProgress' event
 *
 * @class AssetLoader
 * @constructor
 * @uses EventTarget
 * @param assetURLs {Array(String)} An array of image/sprite sheet urls that you would like loaded
 *      supported. Supported image formats include 'jpeg', 'jpg', 'png', 'gif'. Supported
 *      sprite sheet data formats only include 'JSON' at this time. Supported bitmap font
 *      data formats include 'xml' and 'fnt'.
 * @param crossorigin {Boolean} Whether requests should be treated as crossorigin
 */
PIXI.AssetLoader = function(assetURLs, crossorigin)
{
    /**
     * The array of asset URLs that are going to be loaded
     *
     * @property assetURLs
     * @type Array(String)
     */
    this.assetURLs = assetURLs;

    /**
     * Whether the requests should be treated as cross origin
     *
     * @property crossorigin
     * @type Boolean
     */
    this.crossorigin = crossorigin;

    /**
     * Maps file extension to loader types
     *
     * @property loadersByType
     * @type Object
     */
    this.loadersByType = {
        'jpg':  PIXI.ImageLoader,
        'jpeg': PIXI.ImageLoader,
        'png':  PIXI.ImageLoader,
        'gif':  PIXI.ImageLoader,
        'webp': PIXI.ImageLoader,
        'json': PIXI.JsonLoader,
        'atlas': PIXI.AtlasLoader,
        'anim': PIXI.SpineLoader,
        'xml':  PIXI.BitmapFontLoader,
        'fnt':  PIXI.BitmapFontLoader
    };
};

PIXI.EventTarget.mixin(PIXI.AssetLoader.prototype);

/**
 * Fired when an item has loaded
 * @event onProgress
 */

/**
 * Fired when all the assets have loaded
 * @event onComplete
 */

// constructor
PIXI.AssetLoader.prototype.constructor = PIXI.AssetLoader;

/**
 * Given a filename, returns its extension.
 *
 * @method _getDataType
 * @param str {String} the name of the asset
 */
PIXI.AssetLoader.prototype._getDataType = function(str)
{
    var test = 'data:';
    //starts with 'data:'
    var start = str.slice(0, test.length).toLowerCase();
    if (start === test) {
        var data = str.slice(test.length);

        var sepIdx = data.indexOf(',');
        if (sepIdx === -1) //malformed data URI scheme
            return null;

        //e.g. 'image/gif;base64' => 'image/gif'
        var info = data.slice(0, sepIdx).split(';')[0];

        //We might need to handle some special cases here...
        //standardize text/plain to 'txt' file extension
        if (!info || info.toLowerCase() === 'text/plain')
            return 'txt';

        //User specified mime type, try splitting it by '/'
        return info.split('/').pop().toLowerCase();
    }

    return null;
};

/**
 * Starts loading the assets sequentially
 *
 * @method load
 */
PIXI.AssetLoader.prototype.load = function()
{
    var scope = this;

    function onLoad(evt) {
        scope.onAssetLoaded(evt.data.content);
    }

    this.loadCount = this.assetURLs.length;

    for (var i=0; i < this.assetURLs.length; i++)
    {
        var fileName = this.assetURLs[i];
        //first see if we have a data URI scheme..
        var fileType = this._getDataType(fileName);

        //if not, assume it's a file URI
        if (!fileType)
            fileType = fileName.split('?').shift().split('.').pop().toLowerCase();

        var Constructor = this.loadersByType[fileType];
        if(!Constructor)
            throw new Error(fileType + ' is an unsupported file type');

        var loader = new Constructor(fileName, this.crossorigin);

        loader.on('loaded', onLoad);
        loader.load();
    }
};

/**
 * Invoked after each file is loaded
 *
 * @method onAssetLoaded
 * @private
 */
PIXI.AssetLoader.prototype.onAssetLoaded = function(loader)
{
    this.loadCount--;
    this.emit('onProgress', { content: this, loader: loader });
    if (this.onProgress) this.onProgress(loader);

    if (!this.loadCount)
    {
        this.emit('onComplete', { content: this });
        if(this.onComplete) this.onComplete();
    }
};