JavaScript Array Methods You Should Know

Why Array Methods Matter

Modern JavaScript gives you built-in methods that replace most manual for loops for transforming and filtering data. Learning these five will cover the vast majority of everyday tasks.

map() — Transform Every Item

map() returns a new array where each item has been transformed by a function you provide.

const prices = [100, 200, 300]; const withTax = prices.map(p => p * 1.18); console.log(withTax); // [118, 236, 354]

filter() — Keep Only What Matches

const ages = [12, 18, 25, 16, 30]; const adults = ages.filter(age => age >= 18); console.log(adults); // [18, 25, 30]

reduce() — Collapse to a Single Value

reduce() is the most powerful and most confusing at first. It walks through the array, accumulating a result.

const cart = [250, 400, 150]; const total = cart.reduce((sum, price) => sum + price, 0); console.log(total); // 800

find() and some()/every()

const users = [{id: 1, active: true}, {id: 2, active: false}]; const first = users.find(u => u.active); // the object itself const anyActive = users.some(u => u.active); // true const allActive = users.every(u => u.active); // false

Chaining Methods

Because each method returns a new array, you can chain them for readable pipelines:

const result = [1,2,3,4,5,6] .filter(n => n % 2 === 0) .map(n => n * 10); console.log(result); // [20, 40, 60]

Practice Exercise

Given an array of order objects {amount, status}, use filter and reduce to calculate the total amount of only the “completed” orders.