Javascript - Array reduce() Method

Description

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.

Syntax

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

Parameter Values

Parameter	Require	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

Return

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

Example

Get the sum of the numbers in the array:

Demo

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

function getSum(total, num) {
    return total + num;
}
console.log( numbers.reduce(getSum) );//from  w ww. j  ava 2 s. 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));