reduce()

const sum = arr => arr.reduce((a, b) => a + b, 0);const sum = array.reduce((accumulator, element) => {
  return accumulator + element;
}, 0);
// An example that will loop through an array adding
// each element to an accumulator and returning it
// The 0 at the end initializes accumulator to start at 0
// If array is [2, 4, 6], the returned value in sum
// will be 12 (0 + 2 + 4 + 6)

const product = array.reduce((accumulator, element) => {
  return accumulator * element;
}, 1);
// Multiply all elements in array and return the total
// Initialize accumulator to start at 1
// If array is [2, 4, 6], the returned value in product
// will be 48 (1 * 2 * 4 * 6)var array = [36, 25, 6, 15];

array.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue;
}, 0); // 36 + 25 + 6 + 15 = 82function getArraySum(a){
    var total=0;
    for(var i in a) { 
        total += a[i];
    }
    return total;
}

var payChecks = [123,155,134, 205, 105]; 
var weeklyPay= getArraySum(payChecks); //sums up to 722/* this is our initial value i.e. the starting point*/
const initialValue = 0;

/* numbers array */
const numbers = [5, 10, 15];

/* reducer method that takes in the accumulator and next item */
const reducer = (accumulator, item) => {
  return accumulator + item;
};

/* we give the reduce method our reducer function
  and our initial value */
const total = numbers.reduce(reducer, initialValue)
const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15