FontLoader.js

var FontsLoader = global.FontsLoader = function (loadAsParallel) {
        this._loadAsParallel = loadAsParallel || true;
        this._currentProcesses = [];
        this._queue = [];
    };

    FontsLoader.prototype.load = function (fontUrl, mimeType) {
        if (this._loadAsParallel || !this._currentProcesses.length) {
            return this._loadFont(fontUrl, mimeType);
        }
        return this._addToQueue(fontUrl, mimeType);
    };

    FontsLoader.prototype._loadFont = function (fontUrl, mimeType, queueDefer) {
        this._currentProcesses.push(fontUrl);

        var defer = queueDefer || $.Deferred(),
            self = this,
            preloadLink = document.createElement("link"),
            firstLink = document.getElementsByTagName("link")[0],
            insert = function () {
                firstLink.parentNode.insertBefore(preloadLink, firstLink);
            },
            onLoad = function () {
                console.log('Font loaded:', fontUrl);
                var index = self._currentProcesses.indexOf( fontUrl );
                if (index >= 0) {
                    self._currentProcesses.splice(index, 1);
                }
                if (self._queue.length) {
                    self._loadFont.apply(self, this._queue.shift());
                }
                defer.resolve(fontUrl);
            };

        preloadLink.href = fontUrl;
        preloadLink.rel = "preload";
        preloadLink.as = "font";
        preloadLink.crossorigin = "anonymous";
        insert();
        if (mimeType) {
            preloadLink.type = mimeType;
        }
        if (preloadLink.addEventListener) {
            preloadLink.addEventListener('load', onLoad);
        } else {
            preloadLink.onload = onLoad;
        }
        return defer;
    };

    FontsLoader.prototype._addToQueue = function (fontUrl, mimeType) {
        var defer = $.Deferred();
        this._queue.push([ fontUrl, mimeType, defer ]);
        return defer;
    };