Learn JavaScript through the jquery source code (II)

1. anonymous functions

(Function (window, undefined) {}) (window)

The reason for passing in the window variable is that the window is changed from a global variable to a local variable, and the scope chain is not returned to the top-level scope for faster access to the window.

Reasons for increasing undefined in the argument list: Make sure that undefined is really undefined in the scope of the self-invocation of the anonymous function.

Benefits:

To create a private namespace, methods and variables within a function body do not affect global space, and do not conflict with other program variables and methods, which are legendary non-polluting global variables.

2. function extension.

(function (window, undefined) {    var jquery = function ()      {        return new jquery.fn.init ();     }    jQuery.fn = jQuery.prototype = {                 version:  ' 1.8.3 ',         init: function ()          {            return this;         }    }     jquery.fn.init.prototype = jquery.fn;    jquery.extend =  Jquery.fn.extend = function (obj) {        for (var n  in obj)             this[n] = obj[n];        return  This;    }    jquery.fn.extend ({         test: function () {             Console.log (' hello world!! ');         }    });     Window.jquery = window.$ = jquery;}) (window)

Learn JavaScript through the jquery source code (II)