How to copy objects in Javascript

Methods for copying objects in Javascript: 1. Traverse the properties of the original object and assign them to a new object; 2. Change the object into a string, and then into a json object; 3. Concat an empty object Array; 4. Implement deep copy of object through expansion operator; 5. Implement deep copy of array through ES6 expansion operator.

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

How to copy an object in js?

Method 1:

Traverse the properties of the original object and assign them to a new object.

//深复制对象方法    
var cloneObj = function (obj) {  
    var newObj = {};  
    if (obj instanceof Array) {  
        newObj = [];  
    }  
    for (var key in obj) {  
        var val = obj[key];  
        //newObj[key] = typeof val === 'object' ? arguments.callee(val) : val; //arguments.callee 在哪一个函数中运行，它就代表哪个函数, 一般用在匿名函数中。  
        newObj[key] = typeof val === 'object' ? cloneObj(val): val;  
    }  
    return newObj;  
};  
//测试    
var obj = {a:function(){console.log(this.b.c)},b:{c:1}},//设置一个对象  
newObj = cloneObj(obj);//复制对象  
newObj.b.c=2;//给新对象赋新值  
obj.a();//1，不受影响  
newObj.a();//2

Method 2:

1). First change the object into a string, and then into a json object to prevent the object pointer from pointing to the problem, which is a deep copy

2). Properties of undefined and function types will be ignored, while properties of Date type will be converted to strings

var obj = {a:1,b:2}  
var newObj = JSON.parse(JSON.stringify(obj));  
newObj.a=3;  
console.log(obj);  
console.log(newObj);

Method 3:

Methods for array objects, Use the array method to concat an empty array

var a=[1,2,3];  
var b=a;  
var c=[].concat(a);  
a.push(4);  
console.log(b);  
console.log(c);

Method 4:

Extension operator to implement deep copy of the object

var obj = {
  name: 'FungLeo',
  sex: 'man',
  old: '18'}var { ...obj2 } = obj
obj.old = '22'console.log(obj)
console.log(obj2)

Method 5:

ES6 expansion operator implements deep copy of array

var arr = [1,2,3,4,5]var [ ...arr2 ] = arr
arr[2] = 5console.log(arr)
console.log(arr2)

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