Array Unshift in JavaScript

Mar 4, 2022

The unshift() function adds one or more elements to the beginning of the array and returns the new length of the array.

const array = [3, 4, 5];
array.unshift(1, 2); // 5
array; // 1, 2, 3, 4, 5

If you want to unshift an array, unshift([1, 2]) will add [1, 2] as the first element of the array. unshift() does not flatten arrays.

const array = [3, 4, 5];
array.unshift([1, 2]); // 4
array; // [[1,2], 3, 4, 5]

If you want to unshift the elements of an array, you should use the spread operator as shown below.

const array = [3, 4, 5];
const array2 = [1, 2];
array.unshift(...array2); // 5
array; // 1, 2, 3, 4, 5

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