---
title: "JavaScript ES6+ Cheatsheet | FindUtils"
description: "Modern JavaScript syntax: destructuring, arrow functions, promises, modules, and built-in methods"
url: https://findutils.com/cheatsheets/javascript-es6/
---

# JavaScript ES6+ Cheatsheet

Modern JavaScript syntax: destructuring, arrow functions, promises, modules, and built-in methods 59 commands in 9 sections, filed under [Programming](https://findutils.com/cheatsheets/programming/).

## Variables & Declarations

- `const x = 1`: Block-scoped, read-only constant
- `let y = 2`: Block-scoped variable
- `const [a, b] = [1, 2]`: Array destructuring
- `const { name, age } = obj`: Object destructuring
- `const { name: n } = obj`: Destructuring with rename
- `const { x = 10 } = obj`: Destructuring with default

## Arrow Functions

- `const fn = (a, b) => a + b`: Arrow function (implicit return)
- `const fn = (a) => { return a * 2 }`: Arrow function with body
- `const fn = a => a * 2`: Single param (no parens needed)
- `arr.map(x => x * 2)`: Arrow function as callback
- `arr.filter(x => x > 5)`: Filter with arrow function

## Template Literals & Strings

- `` `Hello ${name}` ``: Template literal with interpolation
- `` `multi\nline` ``: Multi-line string
- `str.includes("sub")`: Check if string contains substring
- `str.startsWith("pre")`: Check if starts with
- `str.endsWith("suf")`: Check if ends with
- `str.repeat(3)`: Repeat string n times
- `str.padStart(5, "0")`: Pad string from start
- `str.trimStart() / str.trimEnd()`: Trim whitespace from start/end

## Spread & Rest

- `[...arr1, ...arr2]`: Spread arrays (merge)
- `{ ...obj1, ...obj2 }`: Spread objects (merge)
- `const [first, ...rest] = arr`: Rest in destructuring
- `function fn(...args) {}`: Rest parameters
- `fn(...args)`: Spread as function arguments

## Array Methods

- `arr.map(fn)`: Transform each element
- `arr.filter(fn)`: Keep elements matching condition
- `arr.reduce(fn, init)`: Reduce to single value
- `arr.find(fn)`: Find first matching element
- `arr.findIndex(fn)`: Find index of first match
- `arr.some(fn)`: Test if any element matches
- `arr.every(fn)`: Test if all elements match
- `arr.includes(val)`: Check if value exists
- `arr.flat(depth)`: Flatten nested arrays
- `arr.flatMap(fn)`: Map then flatten one level
- `Array.from(iterable)`: Create array from iterable
- `structuredClone(obj)`: Deep clone object/array

## Objects & Classes

- `{ name, age }`: Shorthand property names
- `{ [key]: value }`: Computed property names
- `{ method() {} }`: Shorthand method
- `Object.keys(obj)`: Get array of keys
- `Object.values(obj)`: Get array of values
- `Object.entries(obj)`: Get array of [key, value] pairs
- `Object.assign({}, obj)`: Shallow copy / merge objects
- `obj?.nested?.prop`: Optional chaining
- `val ?? defaultVal`: Nullish coalescing

## Promises & Async

- `new Promise((resolve, reject) => {})`: Create a promise
- `promise.then(fn).catch(fn)`: Handle promise result/error
- `async function fn() {}`: Async function declaration
- `const result = await promise`: Await promise resolution
- `Promise.all([p1, p2])`: Wait for all promises
- `Promise.allSettled([p1, p2])`: Wait for all (resolved or rejected)
- `Promise.race([p1, p2])`: First promise to settle wins

## Modules

- `export const x = 1`: Named export
- `export default fn`: Default export
- `import { x } from "./mod"`: Named import
- `import fn from "./mod"`: Default import
- `import * as mod from "./mod"`: Import all as namespace
- `const mod = await import("./mod")`: Dynamic import

## Sources

- `https://tc39.es/ecma262/multipage/`: TC39 ECMAScript specification: language syntax and built-in behavior.

## Related

- Cheatsheet: [Barcode Formats](https://findutils.com/cheatsheets/barcode-formats/)
- Cheatsheet: [Python Essentials](https://findutils.com/cheatsheets/python-essentials/)
- Cheatsheet: [Regular Expressions](https://findutils.com/cheatsheets/regex/)