How to Append an Item to an Array With JavaScript

Learn a couple of ways to append items to an array with JavaScript

To append an item to an array, you can either use JavaScript’s push() method or the concat() method, depending on the context. Both methods are provided by the JavaScript Array object.

I’ll show you how and why to use both methods in practice.

Append a single item to an array

Let’s append a vegetable to an existing list (array) of vegetables:

const vegetables = ["broccoli", "onion", "spinach"]

Now you can print out the result:

// ["broccoli", "onion", "spinach", "carot"]

Note: the vegetables array has been modified.

Append multiple items to an array

To append multiple items to an array, you can also use push(), you just add multiple arguments, separated by commas:

const vegetables = ["broccoli", "onion", "spinach"]
vegetables.push("carot", "green beans", "kale")

Note: the vegetables array has been modified.

Modify Array vs. New Array / push() vs. concat()

As noted above, the push() method modifies the original array. If you instead want to create a new array based on the original, and append new item(s) to that, then use the JavaScript Array concat() method:

const vegetables = ["broccoli", "onion", "spinach"]
const newVegetables = vegetables.concat("carot")

Now try to print out both variables:

// ["broccoli", "onion", "spinach"]
// ["broccoli", "onion", "spinach", "carot", "green beans", "kale"]

And you can see that the original vegetables array is unchanged, and newVegetables contains a copy of the vegetables array + the carot we added to it with the concat() method.

The concat() method works the same with multiple items, you just separate them with commas, just like you did with the push() example earlier:

const vegetables = ["broccoli", "onion", "spinach"]
const newVegetables = vegetables.concat("carot", "green beans", "kale")

In summary:

It’s important to not confuse the two array methods, so here’s a final reminder:

  • push() modifies the original array
  • concat() returns (creates) a new array

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