Javascript - Array reduce() Method

The reduce() method will reduce the array to a single value.


The reduce() method will reduce the array to a single value.

The reduce() method executes a function for each value of the array from start to end.

The return value of the function is stored in an accumulator variable.

The reduce() does not run the function for array elements without values.


array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

Parameter Values

ParameterRequire Description
function(total,currentValue, currentIndex,arr) Required. A function to be run for each element in the array.
initialValue Optional. A value to be passed to the function as the initial value

function(total,currentValue, currentIndex,arr)

Argument Require Description
total Required. The initialValue, or the previously returned value of the function
currentValue Required. The value of the current element
currentIndex Optional. The array index of the current element
arr Optional. The array object the current element belongs to


Returns the accumulated result from the last call of the callback function


Get the sum of the numbers in the array:


var numbers = [65, 44, 12, 4];

function getSum(total, num) {
    return total + num;
console.log( numbers.reduce(getSum) );//from w w  w . ja  v  a2s .  c  om

//Round all the numbers in an array, and display the sum:

var numbers = [15.5, 2.3, 1.1, 4.7];

function getSum1(total, num) {
    return total + Math.round(num);
console.log( numbers.reduce(getSum1, 0));