Detailed explanation of function declaration and call in JavaScript

In JavaScript, functions exist as first-class members. Therefore, it is very necessary to master the knowledge of functions in JavaScript. In the past few days, I have read the first part of Chapter 3 and Chapter 4 of JavaScript Ninja. A summary.

JavaScript function declaration:

JavaScript functions are declared using function literals to create functions.

Shaped like

function name(arg1,arg2)//函数的名称可选
{
　　code;
};

Function scope:

There is no block-level scope in JavaScript, only function scope. That is to say, in JavaScript, scope is declared by functions, not by code blocks.

{var a=10;
}
console.log(a);//结果是10

function a()
{var a=10;
}
console.log(a);//结果是undefined

Function call:

1. Call as a function

function a()
{};
a();

2. Call as a method

var o={};
o.haha=function();
haha();

3. Call as a constructor

function Pig()
{};var xiaohong=new Pig();var xiaoming=new Pig();

4. Call using the apply and call methods

function haha()
{};var hahaha1={};var hahaha2={};
haha.apply(hahaha1,[1,2,3,4]);//apply方法第一个参数是函数上下文的对象，第二个参数是要传入参数的数组haha.call(hahaha2,1,2,3,4);call方法的第一个参数是函数上下文的对象，剩下的参数是要传入的参数

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