jQuery中extend函数详解

jQuery.extend(): Merge the contents of two or more objects together into the first object.(把两个或者更多的对象合并到第一个当中)
jQuery.fn.extend():Merge the contents of an object onto the jQuery prototype to provide new jQuery instance methods.(把对象挂载到jQuery的prototype属性，来扩展一个新的jQuery实例方法)

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都会被选择

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是传递过来扩展到this上的对象
var target= this ;
for ( var name in obj){
//name为对象属性
//copy为属性值
copy=obj[name];
//防止循环调用
if (target === copy) continue ;
//防止附加未定义值
if ( typeof copy === 'undefined' ) continue ;
//赋值
target[name]=copy;
}
return target;
}

jQuery.extend = jQuery.fn.extend = function () {
// 定义默认参数和变量
// 对象分为扩展对象和被扩展的对象
//options 代表扩展的对象中的方法
//name 代表扩展对象的方法名
//i 为扩展对象参数起始值
//deep 默认为浅复制
var options, name, src, copy, copyIsArray, clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false ;
//对接下来的参数进行处理
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;
}
//对从i开始的多个参数进行遍历
for ( ; i < length; i++ ) {
// 只处理有定义的值
if ( (options = arguments[ i ]) != null ) {
// 展开扩展对象
for ( name in options ) {
src = target[ name ];
copy = options[ name ];
// 防止循环引用
if ( target === copy ) {
continue ;
}
// 递归处理深拷贝
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 );
// 不处理未定义值
} else if ( copy !== undefined ) {
//给target增加属性或方法
target[ name ] = copy;
}
}
}
}
//返回
return target;
};