Cloning an Object in Node.js


What is the best way to clone an object in node.js

e.g. I want to avoid the situation where:

var obj1 = {x: 5, y:5};
var obj2 = obj1;
obj2.x = 6;
console.log(obj1.x); // logs 6

The object may well contain complex types as attributes, so a simple for(var x in obj1) wouldn't solve. Do I need to write a recursive clone myself or is there something built in that I'm not seeing?

2/20/2011 11:33:58 PM

Accepted Answer

Possibility 1

Low-frills deep copy:

var obj2 = JSON.parse(JSON.stringify(obj1));

Possibility 2 (deprecated)

Attention: This solution is now marked as deprecated in the documentation of Node.js:

The util._extend() method was never intended to be used outside of internal Node.js modules. The community found and used it anyway.

It is deprecated and should not be used in new code. JavaScript comes with very similar built-in functionality through Object.assign().

Original answer::

For a shallow copy, use Node's built-in util._extend() function.

var extend = require('util')._extend;

var obj1 = {x: 5, y:5};
var obj2 = extend({}, obj1);
obj2.x = 6;
console.log(obj1.x); // still logs 5

Source code of Node's _extend function is in here:

exports._extend = function(origin, add) {
  // Don't do anything if add isn't an object
  if (!add || typeof add !== 'object') return origin;

  var keys = Object.keys(add);
  var i = keys.length;
  while (i--) {
    origin[keys[i]] = add[keys[i]];
  return origin;
8/28/2017 6:48:07 PM

I'm surprised Object.assign hasn't been mentioned.

let cloned = Object.assign({}, source);

If available (e.g. Babel), you can use the object spread operator:

let cloned = { ... source };

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