JavaScript Array reduceRight() Method

The Javascript arr.reduceRight() method in JavaScript is used to convert elements of the given array from right to left to a single value.

Syntax:

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

Parameter: This method accepts five parameters as mentioned above and described below: 

• function(total, currentValue, index, arr): It is the required parameter and is used to run for each element of the array. It contains four parameters which are listed below: 
  • total: It is a required parameter and used to specify the initialValue or the previously returned value of the function.
  • currentValue: It is a required parameter and is used to specify the value of the current element.
  • currentIndex: It is an optional parameter and is used to specify the array index of the current element.
  • arr: It is an optional parameter and is used to specify the array object the current element belongs to.
• initialValue: It is an optional parameter and is used to specify the value to be passed to the function as the initial value.

Below are examples of the Array reduceRight() method. 

Example 1: In this example, we will be using the reduce() method to find the difference between the elements of the array.

Javascript

let arr = [175, 50, 25];

function subofArray(total, num) {
    return total - num;
}
function myGeeks(item) {
    console.log(arr.reduceRight(subofArray));
}
myGeeks()

Output

-200

Example 2: This example uses reduceRight() method to return the difference of all array elements from the right.  

Javascript

let arr = [10, 20, 30, 40, 50, 60];

function subofArray(total, num) {
    return total - num;
}
function myGeeks(item) {
    console.log(arr.reduceRight(subofArray));
}
myGeeks();

Output

-90

Example 3: This example use reduceRight() method to return the round sum of all array elements. The code performs a sum that does not affect by the reduceRight() method. 

Javascript

let arr = [1.5, 20.3, 11.1, 40.7];

function sumofArray(sum, num) {
    return sum + Math.round(num);
}
function myGeeks(item) {
    console.log(arr.reduceRight(sumofArray, 0));
}
myGeeks();

Output

74

We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.

Supported Browsers: The browsers supported by the JavaScript Array reduceRight() method are listed below: 

• Google Chrome 3
• Microsoft Edge 12
• Mozilla Firefox 3.0
• Safari 5
• Opera 10.5
• Internet Explorer 9

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.