map a new array index +1 code example

Example 1: array mdn map

let new_array = arr.map(function callback( currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

Example 2: array map

let numbers = [1, 4, 9]
let roots = numbers.map(function(num) {
    return Math.sqrt(num)
})
// roots is now     [1, 2, 3]
// numbers is still [1, 4, 9]