FPS

fps.js

var fps = {
    startTime : 0,
    frameNumber : 0,
    getFPS : function()
    {
        var d = Date.now();
        var currentTime = (d - this.startTime) / 1000;
        var result = Math.floor(++this.frameNumber / currentTime);
        if(currentTime > 1)
        {
            this.startTime = new Date.now();
            this.frameNumber = 0;
        }
        return result;
    }
};