Array Unshift in JavaScript

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

Unshifting an Array

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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