JS: Does Object.assign() create deep copy or shallow copy

问题

I just came across this concept of

var copy = Object.assign({}, originalObject);

which creates a copy of original object into the "copy" object. However, my question is, does this way of cloning object create a deep copy or a shallow copy?

PS: The confusion is, if it creates a deep copy, then it would be the easiest way to clone an object.

回答1:

Forget about deep copy, even shallow copy isn't safe, if the object you're copying has a property with enumerable attribute set to false.

MDN :

The Object.assign() method only copies enumerable and own properties from a source object to a target object

take this example

var o = {};

Object.defineProperty(o,'x',{enumerable: false,value : 15});

var ob={}; 
Object.assign(ob,o);

console.log(o.x); // 15
console.log(ob.x); // undefined

回答2:

By using Object.assign(), you are actually doing Shallow Copy of your object. Whenever we do an operation like assigning one object to other, we actually perform a shallow copy, i.e. if OBJ1 is an object, modifying it through another object which is OBJ2 will reflect changes in OBJ1 too.

回答3:

It creates a shallow copy, according to this paragraph from MDN:

For deep cloning, we need to use other alternatives because Object.assign() copies property values. If the source value is a reference to an object, it only copies that reference value.

For the purposes of redux, Object.assign() is sufficient because the state of a redux app only contains immutable values (JSON).

回答4:

For small Data structures I see that JSON.stringify() and JSON.parse() work nice.

// store as JSON
var copyOfWindowLocation = JSON.stringify(window.location)
console.log("JSON structure - copy:", copyOfWindowLocation)
// convert back to Javascript Object
copyOfWindowLocation = JSON.parse(copyOfWindowLocation)
console.log("Javascript structure - copy:", copyOfWindowLocation)

回答5:

Other answers are complicated.
Some don't answer the question at all.

Below worked for me

// orignal object with deep keys
var originalObject = {
    k1: "v1",
    k2: "v2",
    deepObj: {
        k3: "v3",
        k4: "v4"
    }
};

// make copies now
var copy1 = JSON.parse(JSON.stringify(originalObject));
var copy2 = JSON.parse(JSON.stringify(originalObject));

Hope that helps.

回答6:

var copy = Object.assign({}, originalObject);

does a shallow copy which is changing the copy reflect changes in your original object also. So to perform deep copy I would recommend the lodash cloneDeep

import cloneDeep from 'lodash/cloneDeep';
var copy = cloneDeep(originalObject);

来源：https://stackoverflow.com/questions/34504682/js-does-object-assign-create-deep-copy-or-shallow-copy

标签

javascript

object

deep-copy

shallow-copy