JavaScript Cheatsheet

JS array methods, async/await, destructuring and modern syntax

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JavaScript Cheatsheet

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📋 Array Methods

Transform each element — returns new array

Keep elements matching condition

Fold array to single value (sum)

First element matching — or undefined

Index of first match — or -1

True if any element matches

True if all elements match

Flatten 2 levels deep

Map then flatten one level

Check if value exists

Remove duplicates

Numeric sort ascending

Sort strings by property

Copy elements index 1–3 (non-destructive)

Remove 2 items at index 1, insert 'x' (mutates)

Last element (negative indexing)

📦 Object Utilities

Array of own enumerable keys

Array of own enumerable values

Array of [key, value] pairs

Build object from [key, value] pairs

Shallow clone + override

Merge objects into new (mutates first arg)

Deep clone (modern — no functions/DOM)

Make object immutable (shallow)

Destructure with rest

Destructure with rename

Destructure with default value

Optional chaining — no error if null

Optional method call

Nullish coalescing — default if null/undefined

⏳ Async / Promises

Fetch and parse JSON

Parallel await — fails if any reject

Parallel — includes failures

First to resolve or reject

First to resolve (ignores rejects)

Async generator

Consume async iterable

Error handling + cleanup

Create promise manually

🔀 Destructuring & Spread

Array destructure, skip element

Array rest element

Object destructure with defaults

Destructure in function params

Swap values

Concat arrays

Spread array as function arguments

⭐ Useful One-Liners

Array → object keyed by field

Remove falsy values from object

Group array by field

Max by property

Shuffle array (Fisher-Yates approximate)

All regex matches, never null

Range 0..n-1

Deep clone (simple objects only)

Encode/decode URL component

Generate UUID v4 (modern browsers)

✨ Modern Syntax

Arrow function with default param

Computed property name

Named import (also works for destructure)

Private field (ES2022)

Safe method call with bind

Short-circuit assignment

Logical OR assignment

Nullish assignment (only if null/undefined)

Logical AND assignment (only if truthy)

Explicit resource management (ES2025)