Array Basics

Syntax

const arr = [item1, item2, item3];
arr[index];
arr.length;

Examples

const fruits = ["apple", "banana", "cherry"];

console.log(fruits[0]);      // "apple" - first element
console.log(fruits[fruits.length - 1]); // "cherry" - last element
console.log(fruits.length);  // 3

fruits[1] = "blueberry"; // arrays are mutable
console.log(fruits); // ["apple", "blueberry", "cherry"]

console.log(Array.isArray([1, 2, 3])); // true
console.log(Array.isArray("hello"));    // false

const fromString = Array.from("abc");
console.log(fromString); // ["a", "b", "c"]

const fromMap = Array.from({ length: 5 }, (_, i) => i * 2);
console.log(fromMap); // [0, 2, 4, 6, 8]

Best practices

• Use array literal syntax [] rather than new Array() for creating arrays - it is more concise and avoids a quirky single-number-argument edge case
• Use Array.isArray() rather than typeof to correctly identify arrays, since typeof reports "object" for both
• Use Array.from() to convert array-like or iterable values (like NodeLists or strings) into real arrays with full method support
• Remember that arrays are objects, so assigning one array variable to another copies the reference, not the contents

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation