callback function Principle:
I'm leaving now, I'll let you know.
This is an asynchronous process, "I go" in the process (function execution), "You" can do anything, "to" (function completed) "Notify You" (callback) after the process
Example
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1. Basic methods
<script language= "javascript" type= "Text/javascript" >
function DoSomething (callback) {
...
Call the callback
Callback (' Stuff ', ' goes ', ' here ');
}
function foo (A, B, c) {
I ' M The callback
Alert (A + "" + B + "" + C);
}
DoSomething (foo);
</script>
Or in the form of an anonymous function
<script language= "javascript" type= "Text/javascript" >
function DoSomething (damsg, callback) {
alert (damsg);
if (typeof callback = = "function")
Callback ();
}
DoSomething ("callback function", function () {
Alert ("Like the callbacks form of JQuery!");
});
</script>
2. Advanced methods
The call method using JavaScript
<script language= "javascript" type= "Text/javascript" >
function Thing (name) {
THIS.name = name;
}
Thing.prototype.doSomething = function (callback) {
Call we callback, but using our own instance as the context
Callback.call (this);
}
function foo () {
alert (this.name);
}
var t = new Thing (' Joe ');
T.dosomething (foo); Alerts "Joe" Via ' foo '
</script>
Pass parameters
<script language= "javascript" type= "Text/javascript" >
function Thing (name) {
THIS.name = name;
}
Thing.prototype.doSomething = function (callback, salutation) {
Call we callback, but using our own instance as the context
Callback.call (this, salutation);
}
function foo (salutation) {
Alert (Salutation + "" + this.name);
}
var t = new Thing (' Joe ');
T.dosomething (foo, ' Hi '); Alerts "Hi Joe" via ' foo '
</script>
Apply pass parameters using JavaScript
<script language= "javascript" type= "Text/javascript" >
function Thing (name) {
THIS.name = name;
}
Thing.prototype.doSomething = function (callback) {
Call we callback, but using our own instance as the context
Callback.apply (this, [' Hi ', 3, 2, 1]);
}
function foo (salutation, three, two, one) {
Alert (salutation + "+ THIS.name +" – "+ Three +" "+ Two +" "+ one);
}
var t = new Thing (' Joe ');
T.dosomething (foo); Alerts "Hi joe–3 2 1" via ' foo '
</script> |
Example
If the provided data source is an integer, for a student's score, when the num<=0, is processed by the bottom, when n>0 is handled by the high-level.
| The code is as follows |
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| Copy the following function and save it to 1.js function f (num,callback) {
if (num<0) {
Alert ("Call low-level function processing!");
Alert ("Score cannot be negative, input error!");
}else if (num==0) {
Alert ("Call low-level function processing!");
Alert ("The student may not have taken the exam!") ");
}else{
Alert ("Call high-level function processing!");
Callback ();
}
} Save the following test.html file with 1.js in a directory: <! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en"
"Http://www.w3.org/TR/html4/loose.dtd"
< Html>
<meta http-equiv= "Content-type" content= "text/html; charset=gb2312"
< Script src= "1.js" type= "Text/javascript" ></SCRIPT>
<title> Untitled document </TITLE>
<script Type= "Text/javascript"
function Test () {
var P=document.getelementbyid (" PP ");
pp.innertext= "";
var Num=document.getelementbyid ("Score"). Value;
F (num,function () {//anonymous high-level processing function
if (num<60) alert ("Not qualified!") ");
Else if (num<=90) alert ("The student has excellent results!") ");
Else alert ("excellent performance for this student!");}
pp.innertext= by since1978 qq558064!
}
</script>
<body>
<p>
Callback Function Example: When the student score is score<=0, it is handled by the bottom, and when score>0, it is handled by the high level.
</p>
Please enter student score <input type= "text" id= "score" >
<input type= "button" onclick= "test () "Value= the results"
<p id= "pp" ></P>
</body>
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