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JavaScript is a cornerstone of modern web development, offering the flexibility to create dynamic and interactive user experiences. Mastering JavaScript can be daunting, given its wide range of features and capabilities. That’s why we’ve created this comprehensive javascript cheatsheet to cover everything you need—from basic syntax to advanced concepts.

Whether you’re a beginner or an experienced developer, this JS cheatsheet is designed to provide quick reference and actionable insights.

JavaScript CheatSheet

Feature	Syntax/Example	Explanation	Notes

Declare Variables let x = 10;
const y = 20; Use let for reassignable variables and const for constants Avoid using var due to scoping issues

Data Types string, number, boolean, object JavaScript supports primitive and reference types Use typeof to check data types

Template Literals `Hello, ${name}` Embed expressions in strings Use backticks for multi-line strings

Functions function name(params) { ... } Define reusable blocks of code Arrow functions: const fn = () => { ... }

Arrow Functions const add = (a, b) => a + b; Shorter syntax for anonymous functions No this binding

Array Methods .push(), .pop(), .map(), .filter() Built-in methods for working with arrays Commonly used for transforming and manipulating arrays

String Methods .length, .slice(), .replace() Built-in methods for string operations Strings are immutable; methods return new strings

Object Destructuring const {a, b} = obj; Extract properties from objects Works with arrays too: const [x, y] = arr;

Spread Operator const newArr = [...arr1, ...arr2]; Expands arrays or objects into individual elements Useful for merging arrays or objects

Rest Operator function sum(...nums) { } Collects arguments into an array Opposite of the spread operator

Conditional Statements if (x > 5) { } else { } Used for decision-making Ternary: condition ? value1 : value2;

Switch Statement switch (key) { case 1: ... } Simplifies multiple conditional checks Use default for unmatched cases

Loops for, while, do...while Iterates over arrays, objects, or numbers Use for...of for arrays and for...in for objects

Event Listeners element.addEventListener('click', fn); Attaches an event handler to an element Use removeEventListener to clean up

Promises new Promise((resolve, reject) => { }); Handles asynchronous operations .then() and .catch() for chaining

Async/Await async function fn() { await promise; } Syntactic sugar for promises Requires async keyword

Error Handling try { ... } catch (err) { ... } Catches runtime errors Use finally for cleanup operations

DOM Manipulation document.querySelector('.class'); Access and modify HTML elements Use .innerHTML or .textContent to update content

Event Delegation parent.addEventListener('click', fn); Use a parent element to handle events for multiple child elements Improves performance when dealing with dynamic elements

Timers setTimeout(fn, ms);
setInterval() Delays or repeats execution Use clearTimeout and clearInterval to stop them

Modules export const x;
import { x } from Reuse code across files Use default export for single-value exports

Classes class MyClass { constructor() { } } Blueprint for creating objects Use extends for inheritance

Fetch API fetch(url).then(res => res.json()); Makes HTTP requests Supports modern promise-based syntax

LocalStorage localStorage.setItem('key', value); Stores key-value pairs persistently Use sessionStorage for temporary storage

Object Methods Object.keys(obj), Object.values(obj) Retrieves keys, values, or entries from an object Iterates objects effectively

Map and Set new Map(), new Set() Efficient data structures for key-value pairs and unique values Use .has() and .add() for checks and additions

Regular Expressions /pattern/.test(string) Matches patterns in strings Use exec() for detailed match results

Short-Circuiting `const x = a b;<br>a && b;`

Nullish Coalescing const x = a ?? b; Returns right operand if left is null or undefined More precise than `

Debouncing const fn = debounce(func, delay); Limits frequency of a function execution Useful for optimizing event handlers

Throttling const fn = throttle(func, delay); Ensures a function runs at most once per specified interval Often used in scroll or resize events

Event Loop

Explains how JS handles async operations

JS uses a single-threaded model with non-blocking asynchronous APIs

Learn tasks, microtasks, and priorities

Arrow Function + This No binding of this in arrow functions Retains this from enclosing context Useful in callbacks

Optional Chaining obj?.prop?.nestedProp Safely accesses nested properties Avoids runtime errors on null or undefined

Dynamic Imports import('./module.js').then(module => { }); Lazily load modules Useful for performance optimization

Optional Parameters function fn(a, b = 10) { } Allows setting default values for function parameters Provides flexibility in function calls

SetTimeout with Arguments setTimeout(fn, ms, arg1, arg2) Passes additional arguments to the callback function Useful for dynamic time-based executions

GlobalThis globalThis.property A standardized way to access the global object Works across environments (browser, Node.js, etc.)

Intl API new Intl.NumberFormat().format(num) Formats numbers, dates, and strings for internationalization Use Intl.DateTimeFormat for date localization

WeakMap and WeakSet new WeakMap(), new WeakSet() Holds objects without preventing garbage collection Ideal for private properties and memory optimization

Symbol Data Type const sym = Symbol('desc'); Creates unique and immutable values Used for creating custom object properties

Proxy Object new Proxy(target, handler) Intercepts and customizes operations on objects Useful for validation, logging, or data binding

BigInt const big = 123n; Represents integers with arbitrary precision Use BigInt for calculations beyond Number.MAX_SAFE_INTEGER

Dynamic Property Keys const obj = { [keyName]: value }; Creates object keys dynamically Enables flexibility in object creation

FAQs

Why is JavaScript important for developers?

JavaScript is a versatile, client-side language that powers interactive web applications. It is crucial for front-end, back-end, and even mobile development.

What are some advanced features included in the cheat sheet?

Features like Promises, Async/Await, Proxy Objects, WeakMap, Symbols, and the Intl API are considered advanced and are covered in the cheat sheet.

Can I use this cheat sheet for ES6+ JavaScript?

Yes, the cheat sheet includes modern JavaScript features introduced in ES6 and later versions, like template literals, arrow functions, and the spread operator.