Summary of JS animation timer knowledge

This article summarizes the usage of timers in JS animation and a summary of related knowledge points. Friends in need can refer to it.

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 and often used in the past;

Usually they do something auxiliary and icing on the cake;

Careful people may find a phenomenon, switching from other tabs to the page with loop animation will cause lag and rapid frame switching;

The problem lies in their internal operating mechanism;

Understand setTimeout

It is recommended to use the function form for the first parameter, the string form will be parsed twice, and eval is the same Question;

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 are 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);

Running mechanism

Example:

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

Reason: Join the queue and block execution.

setTimeout legend:

setInterval legend:

##Existence is reasonable

Parent-child element event bubbles, the parent element needs to be executed first, see example 3;

User-defined callback function, usually triggered before the browser's default action, see example 4;

Example 3:

<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>

Example 4:

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

Understanding requestAnimationFrame

The usage is similar to setTimeout, except that no time parameter is required;

The mechanism is completely different:

1, setTimeout is an asynchronous operation, join the task queue (event loop), when the synchronization code in the js engine thread is executed, it will be taken out from the task queue for execution;

2, raf is the user agent (Browser) An interface developed specifically for animation. The user agent will update animation frames at an appropriate frequency (generally the same as the monitor refresh frequency, 1000/60ms). It will stop frame updates on hidden or inactive pages to save CPU resources;

3, raf example

raf is simple and compatible

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

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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The principle of AJAX—how to achieve asynchronous and partial refresh

Ajax implementation code for passing multiple parameters

Ajax verification username and password example code

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