//淺拷貝，雙向改變,指向同一片內(nèi)存空間
var arr1 = [1, 2, 3];
var arr2 = arr1;
arr1[0] = 'change';
console.log('shallow copy: ' + arr1 + " ); //shallow copy: change,2,3
console.log('shallow copy: ' + arr2 + " ); //shallow copy: change,2,3

function shallowClone(copyObj) {
 var obj = {};
 for ( var i in copyObj) {
 obj[i] = copyObj[i];
 }
 return obj;
}
var x = {
 a: 1,
 b: { f: { g: 1 } },
 c: [ 1, 2, 3 ]
};
var y = shallowClone(x);
console.log(y.b.f === x.b.f);  // true

var x = {
 a: 1,
 b: { f: { g: 1 } },
 c: [ 1, 2, 3 ]
};
var y = Object.assign({}, x);
console.log(y.b.f === x.b.f);  // true

var array = [1,2,3]; 
var array_shallow = array; 
var array_concat = array.concat(); 
var array_slice = array.slice(0); 
console.log(array === array_shallow); //true 
console.log(array === array_slice); //false，“看起來”像深拷貝
console.log(array === array_concat); //false，“看起來”像深拷貝

var array = [1, [1,2,3], {name:"array"}]; 
var array_concat = array.concat();
var array_slice = array.slice(0);
array_concat[1][0] = 5; //改變array_concat中數(shù)組元素的值 
console.log(array[1]); //[5,2,3] 
console.log(array_slice[1]); //[5,2,3] 
array_slice[2].name = "array_slice"; //改變array_slice中對(duì)象元素的值 
console.log(array[2].name); //array_slice
console.log(array_concat[2].name); //array_slice

//例1
var source = { name:"source", child:{ name:"child" } } 
var target = JSON.parse(JSON.stringify(source));
target.name = "target"; //改變target的name屬性
console.log(source.name); //source 
console.log(target.name); //target
target.child.name = "target child"; //改變target的child 
console.log(source.child.name); //child 
console.log(target.child.name); //target child
//例2
var source = { name:function(){console.log(1);}, child:{ name:"child" } } 
var target = JSON.parse(JSON.stringify(source));
console.log(target.name); //undefined
//例3
var source = { name:function(){console.log(1);}, child:new RegExp("e") }
var target = JSON.parse(JSON.stringify(source));
console.log(target.name); //undefined
console.log(target.child); //Object {}

jQuery.extend = jQuery.fn.extend = function() { //給jQuery對(duì)象和jQuery原型對(duì)象都添加了extend擴(kuò)展方法
var options, name, src, copy, copyIsArray, clone,
 target = arguments[0] || {},
 i = 1,
 length = arguments.length,
 deep = false;
 //以上其中的變量：options是一個(gè)緩存變量，用來緩存arguments[i]，name是用來接收將要被擴(kuò)展對(duì)象的key，src改變之前target對(duì)象上每個(gè)key對(duì)應(yīng)的value。
 //copy傳入對(duì)象上每個(gè)key對(duì)應(yīng)的value，copyIsArray判定copy是否為一個(gè)數(shù)組，clone深拷貝中用來臨時(shí)存對(duì)象或數(shù)組的src。
// 處理深拷貝的情況
if ( typeof target === "boolean" ) {
 deep = target;
 target = arguments[1] || {};
 //跳過布爾值和目標(biāo) 
 i++;
}

 
// 控制當(dāng)target不是object或者function的情況
if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
 target = {};
}

// 當(dāng)參數(shù)列表長度等于i的時(shí)候，擴(kuò)展jQuery對(duì)象自身。
if ( length === i ) {
 target = this;
 --i;
}

for ( ; i < length; i++ ) {
 if ( (options = arguments[ i ]) != null ) {
  // 擴(kuò)展基礎(chǔ)對(duì)象
  for ( name in options ) {
   src = target[ name ];
   copy = options[ name ];

   // 防止永無止境的循環(huán)，這里舉個(gè)例子，如var i = {};i.a = i;$.extend(true,{},i);如果沒有這個(gè)判斷變成死循環(huán)了
   if ( target === copy ) {
    continue;
   }
   if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
    if ( copyIsArray ) {
     copyIsArray = false;
     clone = src && jQuery.isArray(src) ? src : [];// 如果src存在且是數(shù)組的話就讓clone副本等于src否則等于空數(shù)組。
    } else {
     clone = src && jQuery.isPlainObject(src) ? src : {};// 如果src存在且是對(duì)象的話就讓clone副本等于src否則等于空數(shù)組。
    }

    // 遞歸拷貝
    target[ name ] = jQuery.extend( deep, clone, copy );

   } else if ( copy !== undefined ) {
    target[ name ] = copy;// 若原對(duì)象存在name屬性，則直接覆蓋掉；若不存在，則創(chuàng)建新的屬性。
   }
  }
 }
}

// 返回修改的對(duì)象
return target;
};

var a={"name":"aaa"};
var b={"name":"bbb"};
a.child=b;
b.parent=a;
$.extend(true,{},a);//直接報(bào)了棧溢出。Uncaught RangeError: Maximum call stack size exceeded

var $ = (function(){
 var types = 'Array Object String Date RegExp Function Boolean Number Null Undefined'.split(' ');
 function type() {
 return Object.prototype.toString.call(this).slice(8, -1);
 }
 for (var i = types.length; i--;) {
  $['is' + types[i]] = (function (self) {
  return function (elem) {
   return type.call(elem) === self;
  };
 })(types[i]);
 }
 return $;
})();//類型判斷

function copy(obj,deep){ 
 if(obj === null || typeof obj !== "object"){ 
  return obj; 
 } 　　　　　
 var name, target = $.isArray(obj) ? [] : {}, value; 
 for(name in obj){ 
  value = obj[name]; 
  if(value === obj) {
  continue;
  }
  if(deep && ($.isArray(value) || $.isObject(value))){
  target[name] = copy(value,deep);
  }else{
  target[name] = value;
  } 
 } 
 return target;
}