JavaScript Complete Guide - A to Z JavaScript Concepts Last Updated : 22 Apr, 2025 Comments Improve Suggest changes Like Article Like Report JavaScript is a lightweight, cross-platform, single-threaded, and interpreted compiled programming language. It is also known as the scripting language for web pages. Some of the key features of JavaScript are:Lightweight and Fast: JavaScript is a lightweight programming language that runs quickly in web browsers.Single-Threaded: It processes tasks one at a time, making it simple to manage, though asynchronous features like Promises help handle multiple tasks simultaneously. Event-Driven: JavaScript is designed to handle events (like clicks or key presses) in web applications.Let's see, all essential JavaScript concepts from A to Z, helping you build a solid understanding of the language.JavaScript A to Z Complete GuideJavaScript for Beginners LevelAn Introduction to JavaScriptIntroduction to JSJS SyntaxJS Add JS file in HTML DocumentJS Versions OutputJS CommentsJS StatementsJS EventsJavaScript Variables and Data TypesJS VariablesJS letJS constJS varDifference between var, let, and const keywords in JSGlobal and Local variables in JSAccess Variables from Another File using JavaScript?JS Data TypesJS Type ConversionJS Type CoercionJS HoistingJavaScript OperatorsJS OperatorsOperator precedence in JSJS Arithmetic OperatorsJS Assignment OperatorsJS Comparison OperatorsJS Logical OperatorsJS Ternary OperatorsJS Bitwise OperatorsJS typeof OperatorJavaScript Conditional FlowJS Ternary OperatorJS if-elseSwitch Case in JSJavaScript LoopsLoops in JSJS For LoopJS While LoopJS for-in LoopJS for…of LoopJS do…while LoopJS Continue StatementJS break and continueJS Errors: Throw and Try to CatchDifference between forEach and for loop in JSJavaScript FunctionFunctions in JSHow to write a function in JS?JS Function CallDifferent ways of writing functions in JSDifference between Methods and Functions in JSExplain the Different Function States in JSPass by Value and Pass by Reference in JSCall by Value Vs Call by Reference in JSJS return StatementJS Nested functionsJS Rest parameterJS Anonymous FunctionsHow to Understand Recursion in JSArrow functions in JSJS Function Complete ReferenceJavaScript StringJS StringJS String Storage()String() ConstructorBuilt-in Strings in JSConvert String to Camel Case Count String Occurrences?String MethodsJoin Array Elements into a StringCreate a String with Multiple Spaces Multi-line Strings in JavaScript Generate All Combinations of a String Create a Function from a String String ReferenceJS DateRemove a Character From a String in JSExtract a Number from a String using JSJavaScript NumbersJS NumbersHow are numbers stored in JS?How to create a Number object using JS JS Number ReferenceJavaScript ObjectsJS ObjectsCreating Objects in JS (4 Different Ways)JS JSON ObjectsJS Object ReferencePush an Array into an Object in JSCheck if a Key Exists in JS ObjectJavaScript ArraysArrays in JSCreate an array of a given size in JSGet the first and last item in an array using JSHow to append an element to an array in JS?Remove elements from a JS ArrayJS Basic Array MethodsBest-Known JS Array MethodsWhat are the Important Array Methods of JS?JS Array ReferenceRemove Duplicate Elements From JS ArrayFilter Object Array Based On AttributesAdd an Object to JS ArrayJS Multidimensional ArrayJS Array forEach() MethodArrayMap() Method In JSArrayFilter() Method In JSArrayReduce() Method In JSJavaScript DateJS Date() ConstructorJS Date constructor PropertyJS Date now() MethodJS Date parse() MethodJS Date UTC() MethodJS Date getDate() MethodJS Date getDay() MethodCheck if Date is Today in JS Check if Date is Between Two Dates in JSJS Date ReferenceJavaScript JSONJS JSONJS JSON ObjectsJS JSON parse() MethodJS JSON stringify() MethodPretty Print JSON in JS Add Element to JSON Object in JS Read JSON file in JSJS JSON Complete ReferenceConvert JSON data to html table using jQueryCheck if a key exists inside a JSON objectJavaScript SetSets in JSHow are elements ordered in a Set in JSHow to iterate over Set elements in JS?How to sort a set in JS?JS Set ReferenceJavaScript MapJS MapWhat is JS Map and how to use it?JS Map ReferenceJavaScript ArrayBufferJS ArrayBuffer() ConstructorJS arrayBuffer byteLength PropertyJS arrayBuffer slice() MethodJS ArrayBuffer isView() MethodJS ArrayBuffer maxByteLength PropertyJS ArrayBuffer resize() MethodJS ArrayBuffer ReferenceJavaScript AtomicsAtomics in JS Atomics.and() In JS JS Atomics or() MethodAtomics.xor() In JS JS Atomics add() MethodJS Atomics compareExchange( ) MethodJS Atomics store() MethodJS Atomics ReferenceJavaScript BigIntJS BigIntJS BigInt() constructor JS BigInt constructor PropertyJS BigInt asIntN() MethodJS BigInt asUintN() MethodJS BigInt toLocaleString() MethodJS BigInt toString() MethodJS BigInt valueOf() MethodJS BigInt ReferenceJavaScript Boolean and DataViewJS Boolean() ConstructorJS Boolean Constructor PropertyJS Boolean valueOf() MethodJS Boolean toString() MethodJS Boolean ReferenceJavaScript GeneratorJS Generator() ConstructorJS Generator constructor PropertyJS Generator next() MethodJS Generator return() MethodJS Generator throw() MethodJS Generator ReferenceJavaScript IntlJS Intl.ListFormat supportedLocalesOf() JS Intl.DateTimeFormat supportedLocalesOf()JS Intl.ListFormat format() JS Intl.ListFormat formatToParts()JS Intl.DateTimeFormat format() JS Intl.Collator supportedLocalesOf() JS Intl.DateTimeFormat formatRangeToParts()JS Intl Complete ReferenceJavaScript Math Use of Math object in JSJS Math ObjectJS Math E PropertyJS Math LN2 PropertyJS Math LN10 PropertyJS Math LOG2E PropertyJS Math LOG10E PropertyJS Math PI PropertyJS Math abs() MethodJS Math acos() Method JS Math acosh() MethodJS Math asin() MethodJS Math asinh() MethodJS Math atan() MethodJS Math atan2() MethodJS Math ReferenceJavaScript RegExpJS RegExp() ConstructorJS RegExp constructor PropertyJS RegExp dotAll PropertyJS RegExp flags PropertyJS RegExp global PropertyJS RegExp hasIndices PropertyJS RegExp exec() MethodJS RegExp test() MethodJS RegExp toString() MethodJS RegExp ReferenceAdvanced JSJavaScript PromiseJS PromiseJS promise resolve() MethodJS Promise all() MethodJS Promise then() MethodJS Promise any() MethodJS Promise race() MethodJS promise reject() MethodPromise vs Callback in JSJS Promise ReferenceJavaScript Proxy/handlerJS Proxy/HandlerJS Proxy() ConstructorJS Proxy revocable() MethodJS Handler apply() MethodJS Handler construct() MethodJS Handler defineProperty() MethodJS Handler get() MethodJS Proxy/handler ReferenceJS file handlingJavaScript ReflectJS ReflectJS Reflect get() MethodJS Reflect getPrototypeOf() MethodJS Reflect isExtensible() MethodJS Reflect getOwnPropertyDescriptor() MethodJS Reflect construct() MethodJS Reflect apply() MethodJS Reflect ReferenceJavaScript SymbolJS Symbol() ConstructorJS Symbol constructor PropertyJS Symbol asyncIterator PropertyJS Symbol description PropertyJS Symbol hasInstance PropertyJS Symbol isConcatSpreadable PropertyJS Symbol Iterator PropertyJS Symbol() MethodJS Symbol keyFor() MethodJS Symbol toString() MethodJS Symbol ReferenceJavaScript WeakMapJS WeakMapJS WeakMap() ConstructorJS WeakMap constructor PropertyJS weakMap delete() MethodJS weakMap get() MethodJS weakMap has() MethodJS weakMap set() MethodJS WeakMap ReferenceJavaScript WeakSetJS WeakSetJS WeakSet() ConstructorJS WeakSet constructor propertyJS weakSet add() MethodJS weakSet delete() MethodJS weakSet has() MethodJS WeakSet ReferenceJavaScript ExpressionsJS this KeywordJS Async/Await FunctionJS Object initializerJS Grouping OperatorJS async function expressionJS RegExp(Regular Expression)JS function* expressionJS Function ExpressionJS class expressionAsynchronous JSPromises in JSJS Expressions Complete ReferenceJavaScript Event LoopUnderstanding the Event LoopCall Stack, Web APIs, Callback QueueMicrotasks vs MacrotasksSetTimeout, SetInterval, and Their Effects on the Event LoopJavaScript Classes And OOPSClasses In JSClasses and Objects in JSHow to create a JS class in ES6this Keyword JSNew Keyword in JSObject Constructor in JSInheritance in JSEncapsulation in JSStatic Methods In JSOOP in JSGetter and Setter in JSJS EventJavaScript ErrorInvalid dateRepeat count must be non-negativeCan’t access lexical declaration`variable’ before initializationInvalid assignment left-hand sideAssignment to undeclared variableReference to undefined property “x”Error Handling in JavaScriptJS Errors Throw and Try to CatchConsole in JSJS Error and Exceptional Handling With ExamplesDebugging in JSWhy cannot we catch errors outside of a function in JS?Unexpected token error for catch JSHow to increase multiple try-catch readability in JS?JS Error Handling: Unexpected TokenJavaScript HTTP Methods Put v/s PatchFetch API in JSUse JavaScript Fetch API to Get DataMake an Ajax call from JavaScript Wait for an API Request to Return in JSClient-Side StorageLocal Storage in JSSession Storage in JSDifference between Local Storage, Session, and CookiesJSON Web Token (JWT)JavaScript Asynchronous ProgrammingCallbacks vs Promises vs Async/AwaitEvent EmittersJavaScript Interview PreparationJS Interview Questions and Answers | Set 1JS Interview Questions and Answers | Set-2JS Interview Questions and Answers | Set 3JavaScript Practice QuizJS Course | Practice Quiz-1JS Course | Practice Quiz-2JS Course | Practice Quiz-3JavaScript Libraries & FrameworksFrontend Libraries: React, Preact, Lodash, Moment.js, jQuery, AxiosBackend Libraries: Socket.io, JWT, Bcrypt, Passport.js, CORSFrontend Frameworks: Vue.js, Angular, Next.js, Nuxt.js, GatsbyBackend Frameworks: Express.js, NestJS, Koa.js, Sails.js, FastifyFullStack Frameworks: Meteor.js, Next.js, Nuxt.js, RedwoodJS Comment More infoAdvertise with us kartik Follow Improve Article Tags : JavaScript Web Technologies A-Z Guides Similar Reads HTML Cheat Sheet HTML (HyperText Markup Language) serves as the foundational framework for web pages, structuring content like text, images, and videos. 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