JS Basics

JavaScript Arrays

Complete guide to JavaScript arrays: creation, methods, iteration, and functional patterns.

JavaScript Arrays

An array is a special variable, which can hold more than one value. Arrays are zero-indexed — the first element is at index 0.

Array Methods

JavaScript arrays have many powerful built-in methods:

Mutation methods (modify original):

  • push(), pop(), shift(), unshift()
  • splice(), sort(), reverse()

Iteration methods (non-mutating):

  • map(), filter(), reduce(), forEach()
  • find(), findIndex(), some(), every()
  • flat(), flatMap()

Modern Array Methods

ES6+ added powerful array methods that enable clean functional programming patterns.

Example

javascript
// Array creation
const fruits = ["apple", "banana", "cherry"];
const numbers = Array.from({length: 5}, (_, i) => i + 1);
// [1, 2, 3, 4, 5]

// Basic operations
fruits.push("date");        // add to end
fruits.pop();               // remove from end
fruits.unshift("avocado");  // add to start
fruits.shift();             // remove from start

// Powerful array methods
const data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// map - transform each element
const squared = data.map(n => n ** 2);

// filter - keep elements matching condition
const evens = data.filter(n => n % 2 === 0);

// reduce - accumulate to single value
const sum = data.reduce((acc, n) => acc + n, 0);

// find - first matching element
const firstBig = data.find(n => n > 5);  // 6

// some / every
const hasNegative = data.some(n => n < 0);  // false
const allPositive = data.every(n => n > 0); // true

// Chaining
const result = data
  .filter(n => n % 2 === 0)
  .map(n => n * 3)
  .reduce((acc, n) => acc + n, 0);
console.log(result);  // 90

// Spread / destructuring
const [first, ...rest] = data;
const combined = [...fruits, "elderberry"];
Try it yourself — JAVASCRIPT