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

Syntax

arr.unshift([element1[, ...[, elementN]]])

The elements to add to the front of the array.

The new length of the array upon which the method was called.

var array = [1, 2, 3, 4, 5];

array.unshift(0);
// If we console.log(array.shift()); the console would output 6.
// array is now [0, 1, 2, 3, 4, 5];

array.unshift([-1]);
// array is now [[-1], 0, 1, 2, 3, 4, 5];

🚀 Run code

Source MDN