reduce

var array = [36, 25, 6, 15];

array.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue;
}, 0); // 36 + 25 + 6 + 15 = 82

function 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

// Array.prototype.reduce()

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

array.reduce(function(acumulador, elementoAtual, indexAtual, arrayOriginal), valorInicial)

[1,2,3,4,5].reduce((acc, current)=>acc+current, 0)

arr.reduce(callback( accumulator, currentValue[, index[, array]] )[, initialValue])

/* 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)

arr.reduce(callback( accumulator, currentValue[, index[, array]] ) {
  // return result from executing something for accumulator or currentValue
}[, initialValue]);

[0, 1, 2, 3, 4].reduce(function(accumulateur, valeurCourante, index, array){
  return accumulateur + valeurCourante;
});

array.reduce(callback( accumulator, valueNow[, index[, array]] )[, initialValue]))