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What are the custom functions of javascript?

青灯夜游Original: 2022-03-28 20:07:032385browse

Custom functions include: 1. Named function, syntax "function function name(){}"; 2. Anonymous function, syntax "var variable name=function(){};"; 3. Object function , the syntax is "var variable name=Function();"; 4. Self-tuning function, which implements the definition and call of the function together.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

A function is a set of delayed actions that can be triggered by events or called in other scripts.

Two types of functions in JavaScript: predefined functions and custom functions

Predefined functions
- [parseInt / parseFloat】string to int/float
- ##【isNaN / isFinite】Detect whether the parameter is a non-numeric value/infinite number
- 【escape / unescape 】Encode/decode string
- 【eval】Execute JavaScript script
- 【alert / confirm / prompt】three warning boxes
Custom function
- [Named function]
  function funcName(){}
- 【Anonymous function】
  var x=function(){};
- var x= Function();
- (function(){}());

##Custom functions

In addition to predefined functions, you can also use custom functions in JavaScript.

When customizing a function, there is no need to declare the parameter type of the function, nor the return type of the function.

JavaScript currently supports the following customization methods:

Named function

Anonymous function
Object function
Self-tuning function

Named functions are defined by the function keyword, followed by the function name and parentheses ().

In the same 3f1c4e4b6b16bbbd69b2ee476dc4f83a2cacc6d41bbb37262a98f745aa00fbf0 tag, the function call can be before or after the function definition.
In different 3f1c4e4b6b16bbbd69b2ee476dc4f83a2cacc6d41bbb37262a98f745aa00fbf0 tags, the definition of the function must precede the call of the function, otherwise the call will be invalid.
The format is as follows:

function funcName([parameters]){
  statements;
  [return 表达式;]
}

2. Anonymous function

The definition format of anonymous functions is basically the same as that of named functions, except No name of the function is provided, and there should be a semicolon; at the end. Since there is no function name, you need to use variables to accept anonymous functions to facilitate subsequent function calls.

The format is as follows:

var x=function([parameters]){
  statements;
  [return 表达式;]
};

3. Object function

JavaScript provides the Function class for defining functions. The format is as follows:

var func1=new Function([parameters],statements;);

Function is a keyword used to define a function, and the first letter must be capitalized.

statements is the function execution body. When there are multiple execution statements, the statements are separated by semicolon;.
4. Self-calling function

Generally, the function itself will not be executed automatically and will only be executed when called. Therefore, JavaScript provides a self-calling function that implements function definition and call together. The format is as follows:

(function([parameters]){
  statements;
  [return 表达式;]
})([params]);

You need to use parentheses () to enclose the self-tuning function and end with a semicolon;

params are actual parameters, data is passed in when the function is called.
Code example:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>test</title>
</head>
<body>
  <input id="btn1" type="button" onclick="button1Event()" value="button1" />
  <input id="btn2" type="button" onclick="button2Event()" value="button2" /><br />
  <input id="a" type="text"/><input id="b" type="text"/><br />
  <input id="sumBtn" type="button" value="x+y" onclick="sum()"/>
  
  <script type="text/javascript">
    function button1Event(){/* 命名函数 */
        alert("命名函数：按钮1被点击！");
    }
    var x=function(){/* 匿名函数 */
        alert("匿名函数：按钮2被点击！");
    }
    button2Event=x;
    
    var y=new Function("a", "b", "return a+b");/* 对象函数 */
    sum=function(){
        var aValue=parseInt(document.getElementById("a").value,10);
        var bValue=parseInt(document.getElementById("b").value,10);
        alert("对象函数："+y(aValue,bValue));
    }
    
    var tema=2;var temb=2;
    (function(a,b){/* 自调函数 */
        alert("自调函数："+(a+b));
    })(tema,temb);
  </script>
</body>
</html>

Effect demonstration:

##【Related recommendations:

javascript video tutorial,

web front-end

】

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