what does unshift do in react js code example

Example 1: js add element to front of array

//Add element to front of array
var numbers = ["2", "3", "4", "5"];
numbers.unshift("1");
//Result - numbers: ["1", "2", "3", "4", "5"]

Example 2: insert element at beginning of array javascript

// 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);