javascript push item to beginning of array

let arr = [4, 5, 6]

arr.unshift(1, 2, 3)
console.log(arr);
// [1, 2, 3, 4, 5, 6]

// Use unshift method if you don't mind mutating issue
// If you want to avoid mutating issue
const array = [3, 2, 1]

const newFirstElement = 4

const newArray = [newFirstElement].concat(array) // [ 4, 3, 2, 1 ]

console.log(newArray);