JS: Array.prototype.unshift

myArray.unshift(new1, new2 …)

Adds items to the beginning of array myArray.

Return the new length.

myArray is modified.

// example of using array.unshift()
const ar = [3,4];

console.log(
    ar.unshift(7, [8], 9)
); // 5

console.log(
    ar
);   // [7, [ 8 ], 9, 3, 4]

Reference

ECMAScript® 2016 Language Specification#sec-array.prototype.shift