What requestAnimationFrame is ?

Animation with traditional way

For creating animation with JavaScript, we use setInterval() and setTimeout(). These functions execute the passed function at given time. And with setInterval, there would execute the function after each given time interval. The following example does console the message after every second.

function draw(){
 console.log(“draw something  after every second”);
}
setInterval( draw, 1000 );

Disadvantages of setInterval/setTimeout

So what are the disadvantages of setInterval/setTimeout. It does not care what is going on CPU/ Browser, enough resource is available or not, if there is low or high battery and if a user is in current tab of browser or in another tab. This stuff is not considered by setInterval/setTimeout.

It goes for executing the assigned task at given time of interval, It does not respect CPU resources, browser’s workload etc. These are the reasons, complex setInterval can cause the problem while other application uses the extensive CPU.  As a result, the browser would be unresponsive or crashed.

To overcome the problem

So get rid of all these issues, we can use requestAnimationFrame function. This API is created by people of Mozilla and adopted by other browser vendors, later.

So it’s basically used to create animation with JavaScript, let’s explore how does this work.

function draw() {
 console.log('Your draw code is executed here..');
 requestAnimationFrame(draw);
}
draw();

The draw method displays the message in a console of your browser. We execute this function by invoking draw();. Inside the draw function, after display the message, new draw() is  invoked by requestAnimationFrame(draw). The requestAnimationFrame does not invoke the draw method unless the browser is ready.  

Above script displays the message with 60 frames per second.  Short description about frame rate is mentioned at last of this article.

What if there is a need of less than 60fps

The below code is same like above(requestAnimationFrame) along the disadvantages of setInterval/setTimeout

setInterval(
 function (){
  console.log('Your draw code is executed here..');
 }, (1000/60)
);

If someone wants the frame rate less than 60, what to do? Not to worry, here is the solution. For example, if you want the 16fps by requestAnimationFrame. You could do something like this.

var fps = 16;
function draw() {
 setTimeout(
  function (){
   console.log('Your draw code is executed here..');
   requestAnimationFrame(draw);
  }, (1000/fps)
 );
}

In this code, we use the setTimeout function inside draw method to achieve the 16 frame rate per second.

There are great benefits of using requestAnimation, it asks the browser if there is the possibility of drawing of next frame, It draws only if possible otherwise it ignores.

Suppose you are using setInterval/setTimeout in your page, now you go to another tab in your browser. Chrome/firefox throttles the animation speed by 1 frame per second. However, it does not stop completely.

Traditional vs New way

If you create the same animation by requestAnimationFrame, then the animation task would be stopped and there are no expenses of CPU for this task while you are in another tab. Less CPU means a long battery for your laptop and mobile.

You can see the two different screenshots, first, is using by setInterval and second is using by requestAnimationFrame

animation with a traditional way

animation with requestAnimationFrame way

You can get the complete example over here. To see the difference, switch the tab after rendering these examples in browser

Frame Rate

By default, there is 60fps rate in  requestionAnimationFrame. With javascript, the frame rate is the rate, on which browser draws screen 60 times per second. In normal, the movie would play with 30fps, which means in one second, there are 30 pictures are summed together and presented like the movie.