Anjan Dutta

Reduce in JavaScript

Reduce in JavaScript

Published On: 27/10/2021

JavaScript reduce method works only on arrays and it returns a single value as the result. It accepts a callback function as the parameter. The callback function is also called a reducer function.

The reduce method executes the reducer function on each element of the array and it passes the return value of the previous operation as the first parameter of the reducer function.

See the below example. It's a function to calculate the sum of all the elements in an array.

const number_list = [17, 20, 13];
const sum = number_list.reduce((previousValue, previousValue) => {
return previousValue + previousValue;

This is the simplest example of the JavaScript reduce funtion.