1const sum = arr => arr.reduce((a, b) => a + b, 0);

1function getArraySum(a){
2    var total=0;
3    for(var i in a) { 
4        total += a[i];
5    }
6    return total;
7}
8
9var payChecks = [123,155,134, 205, 105]; 
10var weeklyPay= getArraySum(payChecks); //sums up to 722

1var array = [36, 25, 6, 15];
2
3array.reduce(function(accumulator, currentValue) {
4  return accumulator + currentValue;
5}, 0); // 36 + 25 + 6 + 15 = 82

1const numbers = [15.5, 2.3, 1.1, 4.7];
2document.getElementById("demo").innerHTML = numbers.reduce(getSum, 0);
3
4function getSum(total, num) {
5  return total + Math.round(num);
6}

1const sum = array.reduce((accumulator, element) => {
2  return accumulator + element;
3}, 0);
4// An example that will loop through an array adding
5// each element to an accumulator and returning it
6// The 0 at the end initializes accumulator to start at 0
7// If array is [2, 4, 6], the returned value in sum
8// will be 12 (0 + 2 + 4 + 6)
9
10const product = array.reduce((accumulator, element) => {
11  return accumulator * element;
12}, 1);
13// Multiply all elements in array and return the total
14// Initialize accumulator to start at 1
15// If array is [2, 4, 6], the returned value in product
16// will be 48 (1 * 2 * 4 * 6)

1const array1 = [1, 2, 3, 4];
2const reducer = (accumulator, currentValue) => accumulator + currentValue;
3
4// 1 + 2 + 3 + 4
5console.log(array1.reduce(reducer));
6// expected output: 10
7
8// 5 + 1 + 2 + 3 + 4
9console.log(array1.reduce(reducer, 5));
10// expected output: 15