The concept of closures in Javascript

Always say closed package, in fact, I do not know what the closure is what the meaning, today, Baidu found a closed packet of relevant information, reference finishing, hope later can be useful;

Closures are actually a difficult part of the JavaScript language and a feature of the language, and many advanced applications are said to be supported by closures.

First understand the following concepts:

1. Scope of variables

In JavaScript, declaring variables using the var keyword, a little understanding of the students know that the VAR keyword declared variable is a local variable, and vice versa is a local variable

For example:

var text = ' Hello '; Local variables

Text = ' World '; Global variables

Where local variables and global variables are most commonly applied, it is self-evident that they are functions;

：

Local variables:

var x = 1;

function Demo1 () {

alert (x);

}

Demo1 (); Results 1

function Demo1 () {

var x = 1;

}

alert (x); Result error

Global variables:

function Demo1 () {

x = 1;

}

Demo1 ();

alert (x); Results 1

Summary: Declare variables to add Var, responsible, classmate you declare the variable is a global variable!

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2. How to call or use a local variable externally

The simple method is to define a function inside the function; (insert a few words: personal feeling seems to be somewhat similar to some of the processing methods in the object of PHP, simply say, in a class, using protecte in public)

Direct:

function Demo1 () {

var x = 1;

function Demo2 () {

alert (x); Results 1

}

}

Demo1 ();

The concept of closures in Javascript