JavaScript reduceRight() Method

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JavaScript reduceRight() Method

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Example

Calculate the sum of array elements:

var numbers = [65, 44, 12, 4];
function getSum(total, num){
    return total + num;
}
function myFunction(item){
    document.getElementById("demo").innerHTML = numbers.reduceRight(getSum);
}

Output:

Try it yourself »

Definition and Usage

The reduceRight() method functions the same as reduce(), but the difference is that reduceRight() accumulates the array items from the end of the array to the beginning.

Note: reduce() does not execute the callback function for empty arrays.

Browser Support

The numbers in the table specify the first browser version that fully supports the method.

Method	Chrome	Edge	Firefox	Safari	Opera
reduceRight()	Yes	9.0	3.0	4	10.5

Syntax

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

Parameters

Parameter

Description

function(total, currentValue, index, arr)

Required. The function to execute for each array element.
Function parameters:

Parameter	Description
total	Required. The initial value, or the return value from the previous calculation.
currentValue	Required. The current element.
currentIndex	Optional. The index of the current element.
arr	Optional. The array object the current element belongs to.

initialValue

Optional. The initial value to pass to the function.

Technical Details

Return Value:	Returns the calculated result.
JavaScript Version:	ECMAScript 3

More Examples

Example

Subtract each array element from right to left:

Calculated value:

var numbers = [2, 45, 30, 100]; function getSum(total, num) { return total - num; } function myFunction(item) { document.getElementById("demo").innerHTML = numbers.reduceRight(getSum); }

Try it yourself »

Array Object Reference JavaScript Array Object

JavaScript and HTML DOM Reference

JavaScript Boolean Object