JavaScript Cheat Sheet

Modern JavaScript (ES6+) quick reference. Syntax, array methods, async, and DOM. Bookmark this page or print it.

Variables & Types

const x = 1Constant

let x = 1Mutable

typeof xCheck type

String / Number / BooleanPrimitives

null / undefinedEmpty values

Symbol() / BigInt(42)ES6+ types

arr.map(x => x * 2)Transform

arr.filter(x => x > 0)Filter

arr.reduce((a,b) => a+b, 0)Reduce

arr.find(x => x > 5)Find first

arr.some(x => x > 0)Any match

arr.every(x => x > 0)All match

arr.flat()Flatten

arr.sort((a,b) => a-b)Sort

const {a, b} = objDestructure

{...obj, c: 3}Spread

Object.keys(obj)Get keys

Object.values(obj)Get values

Object.entries(obj)Get entries

Object.assign(target, src)Merge

async function f() {}Async function

await promiseAwait

Promise.all([p1, p2])Parallel

Promise.race([p1, p2])Race

try { await f() } catch(e) {}Error handling

fetch(url).then(r => r.json())Fetch API

document.querySelector(sel)Select element

el.addEventListener(ev, fn)Add event

el.classList.add("cls")Add class

el.setAttribute("k", "v")Set attr

document.createElement("div")Create element

el.innerHTML = "html"Set HTML