ES5 Object.assign equivalent

Question

I wanted to do something which is very straight-forward using Object.assign.

var firstObj = {name : "Saba H.", rollNo : 1};
var secondObj = {college : "WCE"};
var wholeObj = Object.assign(firstObj, secondObj);

console.log(wholeObj); // {name : "Saba H.", rollNo : 1, college : "WCE"}

As Object.assign is part of ECMAScript6 harmony proposal and not supported across many browsers, is it possible to do with ES5? If not then is there any micro library?

https://lodash.com/docs#assign based on the very same -- based on the edit, take a look at the lodash source code why not? — Cristian Cavalli, May 28 '15 at 06:02
in [mdn](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) you can see polyfill — Grundy, May 28 '15 at 07:03

Sareskaph · Accepted Answer · 2015-05-28T06:17:37.113

In underscore.js you can use like,

_.extend(firstObj, secondObj);

In jQuery, you can use,

$.extend({},firstObj,secondObj);

In pure javascipt, you can merge n number of objects by using this function:

function mergeObjects() {
    var resObj = {};
    for(var i=0; i < arguments.length; i += 1) {
         var obj = arguments[i],
             keys = Object.keys(obj);
         for(var j=0; j < keys.length; j += 1) {
             resObj[keys[j]] = obj[keys[j]];
         }
    }
    return resObj;
}

score 7 · Answer 2 · answered Mar 05 '18 at 10:51

I found a working polyfill for Object.assign on MDN (awesome, thanks!):

if (typeof Object.assign != 'function') {
  // Must be writable: true, enumerable: false, configurable: true
  Object.defineProperty(Object, "assign", {
    value: function assign(target, varArgs) { // .length of function is 2
      'use strict';
      if (target == null) { // TypeError if undefined or null
        throw new TypeError('Cannot convert undefined or null to object');
      }

      var to = Object(target);

      for (var index = 1; index < arguments.length; index++) {
        var nextSource = arguments[index];

        if (nextSource != null) { // Skip over if undefined or null
          for (var nextKey in nextSource) {
            // Avoid bugs when hasOwnProperty is shadowed
            if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
              to[nextKey] = nextSource[nextKey];
            }
          }
        }
      }
      return to;
    },
    writable: true,
    configurable: true
  });
}

score 3 · Answer 3 · edited Oct 31 '20 at 14:00

3

The pure javascript way:

function mergeObjects() {
  var res = {};
  for (var i = 0; i < arguments.length; i++)
    for (var x in arguments[i])
      res[x] = arguments[i][x];
  return res;
}

Example:

var my_merged_object = mergeObjects(obj1,obj2,...);

edited Oct 31 '20 at 14:00

Jianwu Chen

3,644
3
20
27

answered Feb 20 '19 at 18:24

Stan

111
5

1

You forgot to declare `x` inside the loop. Otherwise, it will be a global variable. – Maciej Bukowski Apr 09 '20 at 15:14
And a hasOwnProperty check is also missing (second for loop) – René Baudisch Apr 08 '21 at 16:05

score 1 · Answer 4 · answered Jan 10 '20 at 07:47

var extend = function ( defaults, options ) {
    var extended = {};
    var prop;
    for (prop in defaults) {
        if (Object.prototype.hasOwnProperty.call(defaults, prop)) {
            extended[prop] = defaults[prop];
        }
    }
    for (prop in options) {
        if (Object.prototype.hasOwnProperty.call(options, prop)) {
            extended[prop] = options[prop];
        }
    }
    return extended;
};

var settings = extend(defaults, options);

ES5 Object.assign equivalent

4 Answers4

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