JavaScript Array Methods in 2026: The Complete Practical Guide

JavaScript Array Methods in 2026: The Complete Practical Guide The Big Four Method Returns Mutates Original map() New array (same length) ❌ No filter() New array (subset) ❌ No reduce() Single value ❌ No find() First match ❌ No map() — Transform Every Item const users = [{name: 'Alice', age: 30}, {name: 'Bob', age: 25}]; // ❌ Old way const names = []; for (const user of users) { names.push(user.name); } // ✅ map const names = users.map(u => u.name); // ['Alice', 'Bob'] // Transform to different shape const cards = users.map(u => ({ title: u.name, subtitle: `${u.age} years old`, id: u.id })); filter() — Keep Only What Matches const products = [ { name: 'Keyboard', price: 150, inStock: true }, { name: 'Mouse', price: 80, inStock: false }, { name: 'Monitor', price: 500, inStock: true }, ]; // Filter by condition const available = products.filter(p => p.inStock); // Keyboard, Monitor const expensive = products.filter(p => p.price > 100); // Keyboard, Monitor // Chain with map