FPS Meter - Returns a function that is used to compute the framerate without the overhead of updating the DOM every frame

fpsMeter.js

/**
 * FPS Meter - Returns a function that is used to compute the framerate without the overhead of updating the DOM every frame.
 * @author Victor B - www.vitim.us
 * @param {element} elm DOM Element to write the framerate
 * @param {number} refresh Updates per second of the DOM
 * @param {function} callback Function called on every DOM update
 * @return {function} Returns a function that will be called inside the loop
 */
function fpsMeter(elm, refresh, callback){
    //var elm;             //element
    //var refresh;         //refresh every x seconds
    
    var compRate = 1;      //compute frame rate every x frames (calculated on the go)
    var frames = 0;        //number of frames since last timing
    var last = 0;          //start Timing 
    
    return function(){
        if(++frames > compRate){
            var now = Date.now();
            var diff = now - last;
            
            if(diff>0){
                var fps = (1000/(diff/frames))<<0;
                last = now;
                frames = 0;
                
                //exponential ramp the next update to match the current refresh rate
                compRate = ((compRate*0.5)+((fps*refresh)*0.5))<<0;
                
                if(elm) elm.innerHTML = fps;
                if(callback) callback.call(fps);
                
                return true;
            }
            else{
                compRate*=2;                
            }
        }
    }
}



/* Example
    
    var f = fpsMeter(fpsDiv, 5000);
    
    //or
    
    var f = fpsMeter(null, 5000, function(fps){
            //console.log(fps);
            fpsDiv.innerHTML = fps;
    });
    
    
    //game loop
    setInterval(function(){
    
        f();
        //do stuff
    
    },1);

*/