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How to add a new item to an object at a specific position with vanilla JS

This morning, Kieran Barker asked me:

Anyone know whether it’s possible to add an item to a specific position inside an object?

So here’s the thing: unlike arrays, objects don’t have an index.

Technically the browser can order them however it wants. If you need a specific order, you’re supposed to use an array

In practical terms, the object order is almost always maintained. If you add a new item to an object, it typically gets added to the end of the object.

var lunch = {
  sandwich: 'turkey',
  drink: 'soda',
  chips: true

// This gets added after "lunch.chips" in the object
lunch.dessert = 'cookie';

To add an item to a specific index in the object, we need to:

  1. Create a new object.
  2. Setup a variable to count the number of loops (since objects don’t have a native index).
  3. Loop through the original object.
  4. If the index variable equals the position you want to insert the new key/value pair into, push that to the new object.
  5. Push the old key/value pairs into the new object.
  6. Increase the index at the end of each loop.

I wrote a small helper function to handle this.

var addToObject = function (obj, key, value, index) {

	// Create a temp object and index variable
	var temp = {};
	var i = 0;

	// Loop through the original object
	for (var prop in obj) {
		if (obj.hasOwnProperty(prop)) {

			// If the indexes match, add the new item
			if (i === index && key && value) {
				temp[key] = value;

			// Add the current item in the loop to the temp obj
			temp[prop] = obj[prop];

			// Increase the count


	// If no index, add to the end
	if (!index && key && value) {
		temp[key] = value;

	return temp;


Here’s how you would use it.

// Original object
var lunch = {
  sandwich: 'turkey',
  drink: 'soda',
  chips: true

// Add to the end of the object
var lunchWithDessert = addToObject(lunch, 'dessert', 'cookie');

// Add between sandwich and drink
var lunchWithTopping = addToObject(lunch, 'topping', 'tomato', 1);

// Immutable copy of lunch
var lunchClone = addToObject(lunch);

Here’s a demo you can play with.