jQuery.extend(): Merge the contents of two or more objects together into the first object.(把兩個(gè)或者更多的對(duì)象合并到第一個(gè)當(dāng)中)
jQuery.fn.extend():Merge the contents of an object onto the jQuery prototype to provide new jQuery instance methods.(把對(duì)象掛載到j(luò)Query的prototype屬性，來擴(kuò)展一個(gè)新的jQuery實(shí)例方法)

jQuery.extend({
sayhello: function (){
console.log( "Hello,This is jQuery Library" );
}
})
$.sayhello(); //Hello, This is jQuery Library
jQuery.fn.extend({
check: function () {
return this .each( function () {
this .checked = true ;
});
},
uncheck: function () {
return this .each( function () {
this .checked = false ;
});
}
})
$( "input[type='checkbox']" ).check(); //所有的checkbox都會(huì)被選擇

jQuery.extend = jQuery.fn.extend = function () {
var options, name, src, copy, copyIsArray, clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false ;
// Handle a deep copy situation
if ( typeof target === "boolean" ) {
deep = target;
target = arguments[1] || {};
// skip the boolean and the target
i = 2;
}
if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
target = {};
}
if ( length === i ) {
target = this ;
--i;
}
for ( ; i < length; i++ ) {
if ( (options = arguments[ i ]) != null ) {
// Extend the base object
for ( name in options ) {
src = target[ name ];
copy = options[ name ];
// Prevent never-ending loop
if ( target === copy ) {
continue ;
}
if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
if ( copyIsArray ) {
copyIsArray = false ;
clone = src && jQuery.isArray(src) ? src : [];
} else {
clone = src && jQuery.isPlainObject(src) ? src : {};
}
target[ name ] = jQuery.extend( deep, clone, copy );
// Don't bring in undefined values
} else if ( copy !== undefined ) {
target[ name ] = copy;
}
}
}
}
// Return the modified object
return target;
};

jQuery.extend = jQuery.fn.extend = function (obj){
//obj是傳遞過來擴(kuò)展到this上的對(duì)象
var target= this ;
for ( var name in obj){
//name為對(duì)象屬性
//copy為屬性值
copy=obj[name];
//防止循環(huán)調(diào)用
if (target === copy) continue ;
//防止附加未定義值
if ( typeof copy === 'undefined' ) continue ;
//賦值
target[name]=copy;
}
return target;
}

jQuery.extend = jQuery.fn.extend = function () {
// 定義默認(rèn)參數(shù)和變量
// 對(duì)象分為擴(kuò)展對(duì)象和被擴(kuò)展的對(duì)象
//options 代表擴(kuò)展的對(duì)象中的方法
//name 代表擴(kuò)展對(duì)象的方法名
//i 為擴(kuò)展對(duì)象參數(shù)起始值
//deep 默認(rèn)為淺復(fù)制
var options, name, src, copy, copyIsArray, clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false ;
//對(duì)接下來的參數(shù)進(jìn)行處理
if ( typeof target === "boolean" ) {
deep = target;
target = arguments[1] || {};
i = 2;
}
if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
target = {};
}
if ( length === i ) {
target = this ;
--i;
}
//對(duì)從i開始的多個(gè)參數(shù)進(jìn)行遍歷
for ( ; i < length; i++ ) {
// 只處理有定義的值
if ( (options = arguments[ i ]) != null ) {
// 展開擴(kuò)展對(duì)象
for ( name in options ) {
src = target[ name ];
copy = options[ name ];
// 防止循環(huán)引用
if ( target === copy ) {
continue ;
}
// 遞歸處理深拷貝
if ( deep && copy &&; ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
if ( copyIsArray ) {
copyIsArray = false ;
clone = src && jQuery.isArray(src) ? src : [];
} else {
clone = src && jQuery.isPlainObject(src) ? src : {};
}
target[ name ] = jQuery.extend( deep, clone, copy );
// 不處理未定義值
} else if ( copy !== undefined ) {
//給target增加屬性或方法
target[ name ] = copy;
}
}
}
}
//返回
return target;
};