JS implements animation timer method

This article mainly shares with you the method of implementing animation timer in JS. Broadly speaking: all visual presentations changed through JS are called animations; for example, interactive feedback of buttons, links and other elements. , in a narrow sense: the visual animation effect produced by continuously calling js functions through timers to change element attributes.

Timer

Timer is the core technology of JavaScript animation;

setTimeout(), setInterval() are well known to everyone and were often used in the past. ;

Usually they do something auxiliary and icing on the cake;

Careful people may find a phenomenon that there is a loop animation when switching from other tabs The page will have freezes and rapid frame switching;

The problem lies in their inner operating mechanism;

Understand setTimeout

The first parameter It is recommended to use the function form, the string form will be parsed twice, and there is the same problem as eval;

There are more than two parameters, there can be more, see example 1;

This points to the problem, see example 2;

The return value is an integer;

clearTimeout(timer) cancels the timer;

setInterval ,clearInterval is the same as above;

Example 1:

setTimeout(function(a,b){ 
 console.log(a+b); 
},1000,1,1)；

Example 2:

var a = 0;
function foo(){
 console.log(this.a);
};
var obj = {
 a : 2,
 foo:foo
}
setTimeout(obj.foo,100);

Operation mechanism

Example:

setTimeout(function(){ 
 console.log(1); 
}); 
console.log(0);

Reason: Join the queue, blocking execution.

setTimeout legend:

setInterval legend:

<p id="myp" style="height: 100px;width: 100px;background-color: pink;"></p>
<script>
myp.onclick = function(){
 setTimeout(function(){
  alert(0);
 })
}
document.onclick = function(){
 alert(1);
}
</script>

<input type="text" id="myInput">
<script>
myInput.onkeypress = function(event) {
 setTimeout(function(){
  myInput.value = myInput.value.toUpperCase();
 });
}
</script>

window.requestAnimFrame = (function(){ 
 return window.requestAnimationFrame || 
   window.webkitRequestAnimationFrame ||   
   window.mozRequestAnimationFrame || 
   function( callback ){  
    window.setTimeout(callback, 1000 / 60);
    };
  })();

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