Javascript - How to clone an object?

问题:

I am confused. I create a copy from myObjOne, than i delete an entry from myObjOne and JS delete the entry in my copy(myObjTwo) too? But why?

  myObjOne = {};
  myObjOne['name'] = 'xxx';
  myObjOne['id'] = 'yyy';
  myObjOne['plz'] = 'zzz';  

  // clone
  myObjTwo = myObjOne;

  // remove something
  delete myObjOne['name'];

  console.dir(myObjTwo);

example http://jsbin.com/itixes/edit#javascript,html

回答1:

Update: Removing Object.create as a method of cloning as indicated in comments.

  myObjTwo = myObjOne;

does not clone. It simply copies the reference.

If you want to clone, you can use JSON.parse and JSON.stringify

var x = {a:{b:{c:{'d':'e'}}}};
var y = JSON.parse(JSON.stringify(x));  //y is a clone of x
console.log(y.a.b.c.d); //prints e
console.log(y === x); //prints false

Warning: As Raynos mentioned in comments, this JSON based clone does not retain methods of the input object in the output object. This solution is good enough if your object does not contain any methods. Methods are properties of a object that are functions. If var obj = {add : function(a,b){return a+b;}} then add is a method of obj.

If you need a solution that supports copying of methods, then go through these SO answers (as pointed out by musefan, Matt and Ranhiru Cooray)

• How do I correctly clone a JavaScript object?
• What is the most efficient way to deep clone an object in JavaScript?

I would suggest How do I correctly clone a JavaScript object?

回答2:

You can use jQuery like so:

var myObjTwo = jQuery.extend(true, {}, myObjOne);

The first argument indicates that we want to make a deep copy of myObjOne.

回答3:

That is not how you clone, that is simply storing the same original object in an extra variable. Maybe this answer will help you

回答4:

Lots of advice on how to make a copy not only of the object and it's properties, but of all the objects referenced by its properties. Here's a version that clones the object without copying it and so that the clone inherits all properties added later except for those shadowed by own properties of the clone:

var cloneOf = (function() {
  function F(){}
  return function(o) {
    F.prototype = o;
    return new F();
  }
}());

Some may recognise the pattern. An example:

var base = {foo:'foo', bar:'bar'};
var baseClone = cloneOf(base);
alert(baseClone.foo);  // foo

回答5:

You can use Object.assign() but be aware of browser support.

More info here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign.

Example:

myObjTwo = Object.assign({}, myObjOne);

回答6:

Your line myObjTwo = myObjOne does not clone myObjOne, it just creates a duplicate reference to the same object!

The actual answer is to use a clone function, perhaps from a library such as underscore.js. But really, it looks like you have some reading and learning to do about the concept of objects and pointers in Javascript.

回答7:

Simple.

var clone=function(o){
      var n= {}.toString.apply(o)=="[object Array]" ? []:{};
      for(i in o)
         n[i]= typeof o[i]=='object' ? clone(o[i]):o[i];
      return n;
 };

Usage:

var x={a:{d:34},b:33};
var y=clone(x);  // clones 'x'

回答8:

With ES6, use the spread operator.

myObjTwo = {...myObjOne}

The spread operator in es6 is just an ellipsis. It creates a copy of the original, even if the original is destroyed