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;
 }
 // Handle case when target is a string or something (possible in deep copy)
 if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
 target = {};
 }
 // extend jQuery itself if only one argument is passed
 if ( length === i ) {
 target = this;
 --i;
 }
 for ( ; i < length; i++ ) {
 // Only deal with non-null/undefined values
 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;
 }
 // Recurse if we're merging plain objects or arrays
 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 : {};
  }
  // Never move original objects, clone them
  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;
 //當(dāng)?shù)谝粋€(gè)參數(shù)為布爾類型是，次參數(shù)定義是否為深拷貝
 //對(duì)接下來的參數(shù)進(jìn)行處理
 if ( typeof target === "boolean" ) {
 deep = target;
 target = arguments[1] || {};
 // 當(dāng)定義是否深拷貝時(shí)，參數(shù)往后移動(dòng)一位
 i = 2;
 }
 // 如果要擴(kuò)展的不是對(duì)象或者函數(shù)，則定義要擴(kuò)展的對(duì)象為空
 if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
 target = {};
 }
 // 當(dāng)只含有一個(gè)參數(shù)時(shí)，被擴(kuò)展的對(duì)象是jQuery或jQuery.fn
 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;
};