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Detailed explanation of JavaScript function basics

高洛峰Original: 2017-02-03 13:15:281055browse

What is a function?

A function is a code segment that completes a certain function

A function is a code segment that can be executed repeatedly

Function is convenient for management and maintenance

Custom function

By function keyword

function function name ([parameters,...]){

Code segment;

return 返回值;
}

Note

Do not include special characters in function names

It is best for function names to have clear meaning

It is best for function names to follow camel case Notation or underscore method

Function names are strictly case-sensitive

If the function name is repeated, it will be overwritten

The function can have parameters or no parameters, and can have one parameter or There can be multiple parameters

The function adds the return value through return. If there is no return, it will return undefined by default

The function will not be called and will not be executed

Anonymous function

Function Expressions can be stored in variables, and variables can also be used as a function

You can pass anonymous functions as parameters to other functions, and the receiving function can complete certain functions through the passed function

You can perform certain one-time tasks through anonymous functions

Through the Function() constructor

Through the built-in JavaScript function constructor (Function()) definition

var myFunction=new Function(&#39;a&#39;,&#39;b&#39;,&#39;return a+b&#39;);
var myFunction=function(a,b){return a+b;};

Note

The above two methods are equivalent

Try to avoid using the new keyword

Source code

<!DOCTYPE html>
<html>
<head>
<meta charSet="utf-8">
<title></title>
</head>
<body>
<Script type="text/javaScript">
// teSt();
function teSt(){
alert(&#39;thiS iS a teSt&#39;);
}
// teSt();
//函数名称严格区分大小写
function TEST(){
alert("hello king");
}
// TEST();
//函数名称重复会产生覆盖
// teSt();
function teSt(){
alert(&#39;hello maizi&#39;);
}
// teSt();
function teSt1(){
alert(&#39;thiS iS teSt1 function&#39;);
}
// alert(teSt1());
function teSt2(){
return null;
return undefined;
return;
return true;
return &#39;thiS iS king&#39;;
return 1.2;
alert(&#39;thiS iS a teSt&#39;);
return 1;
}
// alert(teSt2());
function calc(num1,num2){
return num1+num2;
}
// alert(calc(1,2));
// alert(window.calc(3,5));
// alert(calc(1,2,3,4,5,6));
// function calc1(num1=1,num=2){
// return num1+num2;
// }
function calc1(num1,num2){
num1=num1||1;
num2=num2||2;
return num1+num2;
}
alert(calc1(3,6));
</Script>
</body>
</html>

Running results:

Detailed explanation of JavaScript function basics

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