In this article we will show you few code example on how to use Javasript reduce()
method. It is used to run a function over all the elements of the array and return a final value.
Code Example –
1. Subtracting array numbers using reduce()
–
const numbers = [175, 50, 25];
console.log(numbers.reduce(myFunc));
function myFunc(total, num) {
return total - num;
}
// Output - 100
2. Adding array entries using reduce()
–
const numbers = [15.5, 2.3, 1.1, 4.7];
console.log(numbers.reduce(getSum, 0));
function getSum(total, num) {
return total + Math.round(num);
}
// Output: 24
Source: W3Schools
3. Adding array values using reduce()
through inline function.
const array1 = [1, 2, 3, 4];
// 0 + 1 + 2 + 3 + 4
const initialValue = 0;
const sumWithInitial = array1.reduce(
(previousValue, currentValue) => previousValue + currentValue,
initialValue
);
console.log(sumWithInitial);
// expected output: 10
Source: MDN
4. Removing Duplicate Entries using Reduce()
let ageGroup = [18, 21, 1, 1, 51, 18, 21, 5, 18, 7, 10];
let uniqueAgeGroup = ageGroup.reduce(function (accumulator, currentValue) {
if (accumulator.indexOf(currentValue) === -1) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
console.log(uniqueAgeGroup); // [ 18, 21, 1, 51, 5, 7, 10 ]
Source: Programiz
5. Get total amount of the products in the shopping cart –
let shoppingCart = [
{
product: 'phone',
qty: 1,
price: 500,
},
{
product: 'Screen Protector',
qty: 1,
price: 10,
},
{
product: 'Memory Card',
qty: 2,
price: 20,
},
];
let total = shoppingCart.reduce(function (previousValue, currentValue) {
return previousValue + currentValue.qty * currentValue.price;
}, 0);
// Output: 550
Source: JavascriptTutorial