JavaScript reference

Array.prototype.unshift

Adds elements to the beginning of an array.

Available since: ES3

Syntax

array.unshift(element1, element2, /* … */)

Parameter	Type	Description
element1, …	any	Elements to add to the beginning.

numberThe new length of the array.

Adding to the beginning:

const list = ['b', 'c'];
list.unshift('a');
 
console.log(list);

Output:

[
  "a",
  "b",
  "c"
]

The method returns the new length, not the array:

const list = ['c'];
 
console.log(list.unshift('a', 'b'));
console.log(list.join(''));

Output:

3
abc

The method changes the array itself. To get a new array and keep the old one, use spread: ['a', ...list].

Arrays — What an array is in JavaScript: creating one, indexes, length, changing elements and nested arrays.