JavaScript Guide - JavaScript | MDN * Skip to main content * Skip to search HTML HTML: Markup language HTML reference * Elements * Global attributes * Attributes * See all… HTML guides * Responsive images * HTML cheatsheet * Date & time formats * See all… Markup languages * SVG * MathML * XML CSS CSS: Styling language CSS reference * Properties * Selectors * At-rules * Values * See all… CSS guides * Box model * Animations * Flexbox * Colors * See all… Layout cookbook * Column layouts * Centering an element * Card component * See all… JavaScript JS JavaScript: Scripting language JS reference * Standard built-in objects * Expressions & operators * Statements & declarations * Functions * See all… JS guides * Control flow & error handing * Loops and iteration * Working with objects * Using classes * See all… Web APIs Web APIs: Programming interfaces Web API reference * File system API * Fetch API * Geolocation API * HTML DOM API * Push API * Service worker API * See all… Web API guides * Using the Web animation API * Using the Fetch API * Working with the History API * Using the Web speech API * Using web workers All All web technology Technologies * Accessibility * HTTP * URI * Web extensions * WebAssembly * WebDriver * See all… Topics * Media * Performance * Privacy * Security * Progressive web apps Learn Learn web development Frontend developer course * Getting started modules * Core modules * MDN Curriculum * Check out the video course from Scrimba, our partner Learn HTML * Structuring content with HTML module Learn CSS * CSS styling basics module * CSS layout module Learn JavaScript * Dynamic scripting with JavaScript module Tools Discover our tools * Playground * HTTP Observatory * Border-image generator * Border-radius generator * Box-shadow generator * Color format converter * Color mixer * Shape generator About Get to know MDN better * About MDN * Advertise with us * Community * MDN on GitHub Blog Toggle sidebar * Web * JavaScript * Guide Theme * OS default * Light * Dark English (US) Remember language Learn more * Deutsch * English (US) * Español * Français * 日本語 * 한국어 * Português (do Brasil) * Русский * 中文 (简体) * 正體中文 (繁體) JavaScript Guide The JavaScript Guide shows you how to use JavaScript and gives an overview of the language. If you need exhaustive information about a language feature, have a look at the JavaScript reference . This Guide is divided into the following chapters. In this article * Introduction * Grammar and types * Control flow and error handling * Loops and iteration * Functions * Expressions and operators * Numbers and strings * Representing dates & times * Regular expressions * Indexed collections * Keyed collections * Working with objects * Using classes * Promises * Typed arrays * Iterators and generators * Resource management * Internationalization * JavaScript modules * Advanced topics Introduction Overview: Introduction * About this guide * About JavaScript * JavaScript and Java * ECMAScript * Tools * What's next Grammar and types Overview: Grammar and types * Basic syntax & comments * Declarations * Variable scope * Variable hoisting * Data structures and types * Literals Control flow and error handling Overview: Control flow and error handling * if...else * switch * try / catch / throw * Error objects Loops and iteration Overview: Loops and iteration * for * while * do...while * continue * break * for...in * for...of Functions Overview: Functions * Defining functions * Calling functions * Function scopes and closures * Arguments & parameters * Arrow functions Expressions and operators Overview: Expressions and operators * Assignment & Comparisons * Arithmetic operators * Bitwise & logical operators * Conditional (ternary) operator Numbers and strings Overview: Numbers and strings * Numbers * Number object * Math object * Strings * String object * Template literals Representing dates & times Overview: Representing dates & times * Date object Regular expressions Overview: Regular expressions * Creating a regular expression * Writing a regular expression pattern * Assertions * Character classes * Groups and backreferences * Quantifiers Indexed collections Overview: Indexed collections Keyed collections Overview: Keyed collections * Map * WeakMap * Set * WeakSet Working with objects Overview: Working with objects * Objects and properties * Creating objects * Defining methods * Getter and setter Using classes Overview: Using classes * Declaring a class * Various class features * Extends and inheritance * Why classes? Promises Overview: Promises * Guarantees * Chaining * Error handling * Composition * Timing Typed arrays Overview: Typed arrays Iterators and generators Overview: Iterators and generators * Iterators * Iterables * Generators Resource management Overview: JavaScript resource management * The using and await using declarations * The DisposableStack and AsyncDisposableStack objects * Error handling Internationalization Overview: Internationalization * Date and time formatting * Number formatting * Collation JavaScript modules Overview: JavaScript modules * Exporting * Importing * Default exports * Renaming features * Aggregating modules * Dynamic module loading Advanced topics After you have learned all fundamental features of JavaScript, you can explore some more niche features, or dive deeper into the language's mechanisms and concepts. * Language overview * Data structures * Enumerability and ownership of properties * Inheritance and the prototype chain * Equality comparisons and sameness * Closures * Meta programming * Memory management * Next Help improve MDN Yes No Learn how to contribute This page was last modified on Nov 7, 2025 by MDN contributors . View this page on GitHub • Report a problem with this content Clear filter input * JavaScript * Tutorials and guides * JavaScript Guide * Introduction * Grammar and types * Control flow and error handling * Loops and iteration * Functions * Expressions and operators * Numbers and strings * Representing dates & times * Regular expressions * Indexed collections * Keyed collections * Working with objects * Using classes * Using promises * JavaScript typed arrays * Iterators and generators * Resource management * Internationalization * JavaScript modules * Intermediate * Language overview * JavaScript data structures * Equality comparisons and sameness * Enumerability and ownership of properties * Closures * Advanced * Inheritance and the prototype chain * Meta programming * Memory Management * References * Built-in objects * AbstractModuleSource * AggregateError * Array * ArrayBuffer * AsyncDisposableStack * AsyncFunction * AsyncGenerator * AsyncGeneratorFunction * AsyncIterator * Atomics * BigInt * BigInt64Array * BigUint64Array * Boolean * DataView * Date * decodeURI() * decodeURIComponent() * DisposableStack * encodeURI() * encodeURIComponent() * Error * escape() * eval() * EvalError * FinalizationRegistry * Float16Array * Float32Array * Float64Array * Function * Generator * GeneratorFunction * globalThis * Infinity * Int8Array * Int16Array * Int32Array * InternalError * Intl * isFinite() * isNaN() * Iterator * JSON * Map * Math * NaN * Number * Object * parseFloat() * parseInt() * Promise * Proxy * RangeError * ReferenceError * Reflect * RegExp * Set * SharedArrayBuffer * String * SuppressedError * Symbol * SyntaxError * Temporal * TypedArray * TypeError * Uint8Array * Uint8ClampedArray * Uint16Array * Uint32Array * undefined * unescape() * URIError * WeakMap * WeakRef * WeakSet * Expressions & operators * Addition (+) * Addition assignment (+=) * Assignment (=) * async function expression * async function* expression * await * Bitwise AND (&) * Bitwise AND assignment (&=) * Bitwise NOT (~) * Bitwise OR (|) * Bitwise OR assignment (|=) * Bitwise XOR (^) * Bitwise XOR assignment (^=) * class expression * Comma operator (,) * Conditional (ternary) operator * Decrement (--) * delete * Destructuring * Division (/) * Division assignment (/=) * Equality (==) * Exponentiation (**) * Exponentiation assignment (**=) * function expression * function* expression * Greater than (>) * Greater than or equal (>=) * Grouping operator ( ) * import.meta * import.meta.resolve() * import() * import.source() * in * Increment (++) * Inequality (!=) * instanceof * Left shift (<<) * Left shift assignment (<<=) * Less than (<) * Less than or equal (<=) * Logical AND (&&) * Logical AND assignment (&&=) * Logical NOT (!) * Logical OR (||) * Logical OR assignment (||=) * Multiplication (*) * Multiplication assignment (*=) * new * new.target * null * Nullish coalescing assignment (??=) * Nullish coalescing operator (??) * Object initializer * Operator precedence * Optional chaining (?.) * Property accessors * Remainder (%) * Remainder assignment (%=) * Right shift (>>) * Right shift assignment (>>=) * Spread syntax (...) * Strict equality (===) * Strict inequality (!==) * Subtraction (-) * Subtraction assignment (-=) * super * this * typeof * Unary negation (-) * Unary plus (+) * Unsigned right shift (>>>) * Unsigned right shift assignment (>>>=) * void operator * yield * yield* * Statements & declarations * async function * async function* * await using * Block statement * break * class * const * continue * debugger * do...while * Empty statement * export * Expression statement * for * for await...of * for...in * for...of * function * function* * if...else * import * Import attributes * import source * Labeled statement * let * return * switch * throw * try...catch * using * var * while * with * Functions * Arrow function expressions * Default parameters * get * Method definitions * Rest parameters * set * The arguments object * [Symbol.iterator]() * callee * length * Classes * constructor * extends * Private elements * Public class fields * static * Static initialization blocks * Regular expressions * Backreference: \1, \2 * Buffer boundary assertion: \A, \z, \Z * Capturing group: (...) * Character class escape: \d, \D, \w, \W, \s, \S * Character class: [...], [^...] * Character escape: \n, \u{...} * Disjunction: | * Input boundary assertion: ^, $ * Literal character: a, b * Lookahead assertion: (?=...), (?!...) * Lookbehind assertion: (?<=...), (?<!...) * Modifier: (?ims-ims:...) * Named backreference: \k<name> * Named capturing group: (?<name>...) * Non-capturing group: (?:...) * Quantifier: *, +, ?, {n}, {n,}, {n,m} * Unicode character class escape: \p{...}, \P{...} * Wildcard: . * Word boundary assertion: \b, \B * Errors * AggregateError: No Promise in Promise.any was resolved * Error: Permission denied to access property "x" * InternalError: too much recursion * RangeError: argument is not a valid code point * RangeError: BigInt division by zero * RangeError: BigInt negative exponent * RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD' * RangeError: invalid array length * RangeError: invalid date * RangeError: precision is out of range * RangeError: radix must be an integer * RangeError: repeat count must be less than infinity * RangeError: repeat count must be non-negative * RangeError: x can't be converted to BigInt because it isn't an integer * ReferenceError: "x" is not defined * ReferenceError: assignment to undeclared variable "x" * ReferenceError: can't access lexical declaration 'X' before initialization * ReferenceError: must call super constructor before using 'this' in derived class constructor * ReferenceError: super() called twice in derived class constructor * SyntaxError: 'arguments'/'eval' can't be defined or assigned to in strict mode code * SyntaxError: "0"-prefixed octal literals are deprecated * SyntaxError: "use strict" not allowed in function with non-simple parameters * SyntaxError: "x" is a reserved identifier * SyntaxError: \ at end of pattern * SyntaxError: a declaration in the head of a for-of loop can't have an initializer * SyntaxError: applying the 'delete' operator to an unqualified name is deprecated * SyntaxError: arguments is not valid in fields * SyntaxError: await is only valid in async functions, async generators and modules * SyntaxError: await/yield expression can't be used in parameter * SyntaxError: cannot use ?? unparenthesized within || and && expressions * SyntaxError: character class escape cannot be used in class range in regular expression * SyntaxError: continue must be inside loop * SyntaxError: duplicate capture group name in regular expression * SyntaxError: duplicate formal argument x * SyntaxError: for-in loop head declarations may not have initializers * SyntaxError: function statement requires a name * SyntaxError: functions cannot be labelled * SyntaxError: getter and setter for private name #x should either be both static or non-static * SyntaxError: getter functions must have no arguments * SyntaxError: identifier starts immediately after numeric literal * SyntaxError: illegal character * SyntaxError: import declarations may only appear at top level of a module * SyntaxError: incomplete quantifier in regular expression * SyntaxError: invalid assignment left-hand side * SyntaxError: invalid BigInt syntax * SyntaxError: invalid capture group name in regular expression * SyntaxError: invalid character in class in regular expression * SyntaxError: invalid class set operation in regular expression * SyntaxError: invalid decimal escape in regular expression * SyntaxError: invalid identity escape in regular expression * SyntaxError: invalid named capture reference in regular expression * SyntaxError: invalid property name in regular expression * SyntaxError: invalid range in character class * SyntaxError: invalid regexp group * SyntaxError: invalid regular expression flag "x" * SyntaxError: invalid unicode escape in regular expression * SyntaxError: JSON.parse: bad parsing * SyntaxError: label not found * SyntaxError: missing : after property id * SyntaxError: missing ) after argument list * SyntaxError: missing ) after condition * SyntaxError: missing ] after element list * SyntaxError: missing } after function body * SyntaxError: missing } after property list * SyntaxError: missing = in const declaration * SyntaxError: missing formal parameter * SyntaxError: missing name after . operator * SyntaxError: missing variable name * SyntaxError: negated character class with strings in regular expression * SyntaxError: new keyword cannot be used with an optional chain * SyntaxError: nothing to repeat * SyntaxError: numbers out of order in {} quantifier. * SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code * SyntaxError: parameter after rest parameter * SyntaxError: private fields can't be deleted * SyntaxError: property name __proto__ appears more than once in object literal * SyntaxError: raw bracket is not allowed in regular expression with unicode flag * SyntaxError: redeclaration of formal parameter "x" * SyntaxError: reference to undeclared private field or method #x * SyntaxError: rest parameter may not have a default * SyntaxError: return not in function * SyntaxError: setter functions must have one argument * SyntaxError: string literal contains an unescaped line break * SyntaxError: super() is only valid in derived class constructors * SyntaxError: tagged template cannot be used with optional chain * SyntaxError: Unexpected '#' used outside of class body * SyntaxError: Unexpected token * SyntaxError: unlabeled break must be inside loop or switch * SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**' * SyntaxError: use of super property/member accesses only valid within methods or eval code within methods * SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead * TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed * TypeError: 'x' is not iterable * TypeError: "x" is (not) "y" * TypeError: "x" is not a constructor * TypeError: "x" is not a function * TypeError: "x" is not a non-null object * TypeError: "x" is read-only * TypeError: already executing generator * TypeError: BigInt value can't be serialized in JSON * TypeError: calling a builtin X constructor without new is forbidden * TypeError: can't access/set private field or method: object is not the right class * TypeError: can't assign to property "x" on "y": not an object * TypeError: can't convert BigInt to number * TypeError: can't convert x to BigInt * TypeError: can't define property "x": "obj" is not extensible * TypeError: can't delete non-configurable array element * TypeError: can't redefine non-configurable property "x" * TypeError: can't set prototype of this object * TypeError: can't set prototype: it would cause a prototype chain cycle * TypeError: cannot use 'in' operator to search for 'x' in 'y' * TypeError: class constructors must be invoked with 'new' * TypeError: cyclic object value * TypeError: derived class constructor returned invalid value x * TypeError: getting private setter-only property * TypeError: Initializing an object twice is an error with private fields/methods * TypeError: invalid 'instanceof' operand 'x' * TypeError: invalid Array.prototype.sort argument * TypeError: invalid assignment to const "x" * TypeError: Iterator/AsyncIterator constructor can't be used directly * TypeError: matchAll/replaceAll must be called with a global RegExp * Typ