How to implement asynchronous in javascript
How to implement asynchronous JavaScript: 1. Use the setTimeout method; 2. Use the setImmediate method; 3. Use the requestAnimationFrame method; 4. Monitor the new Image loading status; 5. Monitor the script loading status method.
The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, DELL G3 computer.
Javascript method to implement asynchronousness:
1. setTimeout: This is the simplest
setTimeout( function() {
console.log(1);
});
console.log(2);2 , setImmediate: a new function added by IE10, specifically used to liberate the ui thread. IE10 and below and other browsers do not support
setImmediate(function(){
console.log(1);
});
console.log(2);3. requestAnimationFrame: a new product in the HTML5/CSS3 era, specially used for animation. Low-level browsers do not support
var asynByAniFrame = (function(){
var _window = window,
frame = _window.requestAnimationFrame
|| _window.webkitRequestAnimationFrame
|| _window.mozRequestAnimationFrame
|| _window.oRequestAnimationFrame
|| _window.msRequestAnimationFrame;
return function( callback ) { frame( callback ) };
})();
asynByAniFrame(function(){
console.log(1);
})
console.log(2);4. Monitoring the new Image loading status: Asynchronous implementation is achieved by loading an image in the data:image data format and listening to the loading status.
Although some browsers do not support the data:image image data format, they can still trigger their onerror state to achieve asynchronous implementation. However, for IE8 and below, for images in the data:image data format, onerror is executed synchronously
function asynByImg( callback ) {
var img = new Image();
img.onload = img.onerror = img.onreadystatechange = function() {
img = img.onload = img.onerror = img.onreadystatechange = null;
callback();
}
img.src = "data:image/png,";
}
asynByImg(function(){
console.log(1);
});
console.log(2);5. Monitor the script loading status
The principle is the same as new Image. Generate a data:text/javascript script and monitor its loading status to achieve asynchronous implementation.
Although some browsers do not support scripts in the data:text/javascript format, they can still trigger their onerror and onreadystatechange events to achieve asynchronous implementation.
var asynByScript = (function() {
var _document = document,
_body = _document.body,
_src = "data:text/javascript,",
//异步队列
queue = [];
return function( callback ) {
var script = _document.createElement("script");
script.src = _src;
//添加到队列
queue[ queue.length ] = callback;
script.onload = script.onerror = script.onreadystatechange = function () {
script.onload = script.onerror = script.onreadystatechange = null;
_body.removeChild( script );
script = null;
//执行并删除队列中的第一个
queue.shift()();
};
_body.appendChild( script );
}
})();
asynByScript( function() {
console.log(1);
} );
console.log(2);Related free learning recommendations: javascript(Video)
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