var limitLoop = function (fn, fps) {

    // Use var then = Date.now(); if you
    // don't care about targetting < IE9
    var then = new Date().getTime();

    // custom fps, otherwise fallback to 60
    fps = fps || 60;
    var interval = 1000 / fps;

    return (function loop(time){
        requestAnimationFrame(loop);

        // again, Date.now() if it's available
        var now = new Date().getTime();
        var delta = now - then;

        if (delta > interval) {
            // Update time
            // now - (delta % interval) is an improvement over just
            // using then = now, which can end up lowering overall fps
            then = now - (delta % interval);

            // call the fn
            fn();
        }
    }(0));
};