Open In App

JavaScript Array reduce() Method

Improve
Improve
Improve
Like Article
Like
Save Article
Save
Share
Report issue
Report

The Javascript arr.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left to right) and the return value of the function is stored in an accumulator. 

Syntax: 

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

Parameters:

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 is used to specify the initial value 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.

Return value:

The JavaScript array reduce method returns a single value/element after traversing the complete array.

Below are examples of the Array reduce() method.

Example 1: In this example, we will write a reduce function to simply print the difference of the elements of the array.

Javascript




// Input array
let arr = [175, 50, 25];
 
// Callback function for reduce method
function subofArray(total, num) {
    return total - num;
}
 
//Fucntion to execute reduce method
function myGeeks(item) {
    // Display output
    console.log(arr.reduce(subofArray));
}
myGeeks()


Output

100

Example 2: This example uses reduce() method to return the sum of all array elements. 

Javascript




// Input array
let arr = [10, 20, 30, 40, 50, 60];
// Callback function for reduce method
function sumofArray(sum, num) {
    return sum + num;
}
//Fucntion to execute reduce method
function myGeeks(item) {
    // Display output
    console.log(arr.reduce(sumofArray));
}
myGeeks();


Output

210

 Example 3: This example uses reduce() method to return the round sum of all array elements. 

Javascript




// Input array
let arr = [1.5, 20.3, 11.1, 40.7];
 
// Callback function for reduce method
function sumofArray(sum, num) {
    return sum + Math.round(num);
}
 
//Fucntion to execute reduce method
function myGeeks(item) {
    // Display output
    console.log(arr.reduce(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 JavaScript Array reduce() method are listed below:

  • Google Chrome
  • Microsoft Edge
  • Mozilla Firefox
  • Safari
  • Opera

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.



Last Updated : 17 Jul, 2023
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads