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 . fil