Web Front-endJS TutorialDetailed explanation of how to use callback function (callback) in jqueryDetailed explanation of how to use callback function (callback) in jquery
When I was learning jquery by myself, I saw an English word (Callback), and suddenly a cold sweat broke out on my back. After a quick google, I found that the original Chinese translation was callback. That is Callback function. I didn’t understand, so I googled the callback function and found that the Chinese explanations on the Internet were too “esoteric”. I admitted that I was lacking in talent and knowledge. After reading a few callback examples, I seem to understand it a bit. The following is my understanding of the callback function. If I understand it wrong, please correct me. I am very grateful.
First of all, let’s start with the English definition on the jquery website. As a Chinese, I really feel tragic. The definition of a callback is interpreted by domestic "experts". It just goes around in circles. It seems that he is only an expert if he gets you in. Floating clouds, everything is floating clouds.
A callback is a function that is passed as an argument to another function and is executed after its parent function has completed.
This is the explanation in js, I don’t count the explanation in other languages. explain.
Literally understood, callback is the calling process of a function. So let’s start by understanding this calling process. Function a has one parameter, which is function b. When function a is executed, function b is executed. Then this process is called callback.
In fact, Chinese is also easy to understand: callback, callback, means call back. Finish function a in advance and call function b later.
A real-life example: After the date, you send your girlfriend home. When you say goodbye, you will definitely say: "Send me a message when you get home. I'm worried about you." Right? Then, Your girlfriend actually sent you a message after she got home. Boy, you have a chance.
In fact, this is a callback process. You leave a function b (asking your girlfriend to send you a message) to your girlfriend, and then your girlfriend goes home. The action of going home is function a. She must first return home, execute the content of function a, and then execute function b, and then you will receive a message.
One thing must be clear here: function b is passed to function a in the form of a parameter, then function b is called a callback function.
Maybe someone has questions: Does it have to be passed in the form of parameters? Can't I call function b directly in function a? Indeed it can. Solving.
Understanding examples:
<html>
<head>
<title>回调函数(callback)</title>
<script language="javascript" type="text/javascript">
function a(callback)
{
alert("我是parent函数a！");
alert("调用回调函数");
callback();
}
function b(){
alert("我是回调函数b");
}
function c(){
alert("我是回调函数c");
}
function test()
{
a(b);
a(c);
}
</script>
</head>
<body>
<h1 id="学习js回调函数">学习js回调函数</h1>
<button onClick=test()>click me</button>
<p>应该能看到调用了两个回调函数</p>
</body>
</html>Everyone can use the callback function, but after Jquery encapsulates it, it cannot let everyone understand the true meaning of the callback function. use.
JS Api explains this: A callback is a function that is passed as an argument to another function and is executed after its parent function has completed.
Of course we can actually do it in JS Try the magic of callback functions.
If you call it directly in function a, then this callback function will be restricted. But using functions as parameters has the following benefits: when you do a(b), function b becomes a callback function, and when you can also do a(c), function c becomes a callback function. If you write function a(){...;b();}, you lose the flexibility of variables. Here is the code:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="GBK" />
<title>回调函数(callback)</title>
<script type="text/javascript" src="http://cdn.bootcss.com/jquery/1.9.0/jquery.min.js"></script>
<script language="javascript" type="text/javascript">
var f;
function d(){
alert("我是Jquery定义的函数d");
}
var e = function(){
alert("我也是Jquery定义的函数e");
}
function a(callback) {
alert("我是parent函数a！");
d();
if (typeof callback === "function"){
//alert(callback);
callback();
}
}
function b(){
alert("我是回调函数b");
d();
e();
f();
}
function c(){
alert("我是回调函数c");
d();
e();
f();
}
function test1() {
a(b);
}
function test2() {
a(c);
}
$(function(){
f = function(){
alert("我是回调函数f");
}
});
</script>
</head>
<body >
<h1 id="学习js回调函数">学习js回调函数</h1>
<button onClick=test1()>test a(b)</button>
<button onClick=test2()>test a(c)</button>
<p>应该能看到调用了两个回调函数</p>
<p > </p>
</body>
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