easiest way to sum an array js code example

Example 1: summation js

const summation = (n) => (n * (n + 1)) / 2;

Example 2: Write a function that takes an array of number values and returns the sum.

function amountTotal(amount) {
        var total = 0;
        for (i = 0; i < amount.length; ++i) {
             total += amount[i]; // add each element in an array to total
        }
        return total;// return sum of elements in array
}