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JavaScript array reduce | Method

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JavaScript array reduce() method used to execute a reducer function for the array element. The final result of running the reducer across all elements of the array is a single value.

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

Note: It does not execute the function for empty array elements and does not change the original array.

JavaScript array reduce

Simple example code Sum of All Values of Array.

<!DOCTYPE html>

    const numbers = [1, 2, 3, 4, 5, 6];

    function sum(accumulator, currentValue) {
      return accumulator + currentValue;

    let res = numbers.reduce(sum);




JavaScript array reduce Method

Using the arrow function for same example

let summation = numbers.reduce(
  (accumulator, currentValue) => accumulator + currentValue

console.log(summation); // 21

Typically, we use a for loop to iterate over the elements and add them up as shown in the following example:

let numbers = [1, 2, 3];

let sum = 0;
for (let i = 0; i < numbers.length; i++) {
    sum += numbers[i];

console.log(sum); //6

More JavaScript Array reduce() examples

Suppose that you have the following shoppingCart array of product objects:

let shoppingCart = [
    product: 'phone',
    qty: 1,
    price: 500,
    product: 'Screen Protector',
    qty: 1,
    price: 10,
    product: 'Memory Card',
    qty: 2,
    price: 20,

To calculate the total amount of products in the shopping cart, you can use the reduce() method, like this:

let total = shoppingCart.reduce(function (previousValue, currentValue) {
  return previousValue + currentValue.qty * currentValue.price;
}, 0);

Output: 550

Do comment if you have any doubts or suggestions on this JS array method.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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