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data/mdn-content/files/en-us/web/html
data/mdn-content/files/en-us/web/html/microdata/index.md
--- title: Microdata slug: Web/HTML/Microdata page-type: guide --- {{HTMLSidebar}} Microdata is part of the {{glossary("WHATWG")}} HTML Standard and is used to nest metadata within existing content on web pages. Search engines and web crawlers can extract and process microdata from a web page and use it to provide a ...
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data/mdn-content/files/en-us/web/html
data/mdn-content/files/en-us/web/html/cors_enabled_image/index.md
--- title: Allowing cross-origin use of images and canvas slug: Web/HTML/CORS_enabled_image page-type: guide --- {{HTMLSidebar}} HTML provides a [`crossorigin`](/en-US/docs/Web/HTML/Element/img#crossorigin) attribute for images that, in combination with an appropriate {{Glossary("CORS")}} header, allows images define...
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data/mdn-content/files/en-us/web
data/mdn-content/files/en-us/web/opensearch/index.md
--- title: OpenSearch description format slug: Web/OpenSearch page-type: guide --- {{AddonSidebar}} The **[OpenSearch description format](https://github.com/dewitt/opensearch)** can be used to describe the web interface of a search engine. This allows a website to describe a search engine for itself, so that a browse...
0
data/mdn-content/files/en-us/web
data/mdn-content/files/en-us/web/javascript/index.md
--- title: JavaScript slug: Web/JavaScript page-type: landing-page --- {{jsSidebar}} **JavaScript** (**JS**) is a lightweight interpreted (or [just-in-time](https://en.wikipedia.org/wiki/Just-in-time_compilation) compiled) programming language with {{Glossary("First-class Function", "first-class functions")}}. While ...
0
data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/equality_comparisons_and_sameness/index.md
--- title: Equality comparisons and sameness slug: Web/JavaScript/Equality_comparisons_and_sameness page-type: guide --- {{jsSidebar("Intermediate")}} JavaScript provides three different value-comparison operations: - [`===`](/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality) β€” strict equality (triple e...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/event_loop/the_javascript_runtime_environment_example.svg
<svg xmlns="http://www.w3.org/2000/svg" width="294.708" height="271.079" viewBox="0 0 77.975 71.723"><g style="visibility:visible" class="com.sun.star.drawing.CustomShape"><path style="fill:#cfe7f5;stroke:none" d="M5550 11500H1200V3500h8700v8000z" transform="translate(-10.576 -31.118) scale(.00893)"/><path style="fill:...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/event_loop/index.md
--- title: The event loop slug: Web/JavaScript/Event_loop page-type: guide --- {{jsSidebar("Advanced")}} JavaScript has a runtime model based on an **event loop**, which is responsible for executing the code, collecting and processing events, and executing queued sub-tasks. This model is quite different from models i...
0
data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/data_structures/index.md
--- title: JavaScript data types and data structures slug: Web/JavaScript/Data_structures page-type: guide --- {{jsSidebar("More")}} Programming languages all have built-in data structures, but these often differ from one language to another. This article attempts to list the built-in data structures available in Jav...
0
data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/closures/index.md
--- title: Closures slug: Web/JavaScript/Closures page-type: guide --- {{jsSidebar("Intermediate")}} A **closure** is the combination of a function bundled together (enclosed) with references to its surrounding state (the **lexical environment**). In other words, a closure gives you access to an outer function's scop...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/javascript_technologies_overview/index.md
--- title: JavaScript technologies overview slug: Web/JavaScript/JavaScript_technologies_overview page-type: guide --- {{jsSidebar("Introductory")}} Whereas [HTML](/en-US/docs/Web/HTML) defines a webpage's structure and content and [CSS](/en-US/docs/Web/CSS) sets the formatting and appearance, [JavaScript](/en-US/doc...
0
data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/inheritance_and_the_prototype_chain/index.md
--- title: Inheritance and the prototype chain slug: Web/JavaScript/Inheritance_and_the_prototype_chain page-type: guide --- {{jsSidebar("Advanced")}} In programming, _inheritance_ refers to passing down characteristics from a parent to a child so that a new piece of code can reuse and build upon the features of an e...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/enumerability_and_ownership_of_properties/index.md
--- title: Enumerability and ownership of properties slug: Web/JavaScript/Enumerability_and_ownership_of_properties page-type: guide --- {{jsSidebar("More")}} Every property in JavaScript objects can be classified by three factors: - Enumerable or non-enumerable; - String or [symbol](/en-US/docs/Web/JavaScript/Refer...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/memory_management/index.md
--- title: Memory management slug: Web/JavaScript/Memory_management page-type: guide --- {{jsSidebar("Advanced")}} Low-level languages like C, have manual memory management primitives such as [`malloc()`](https://pubs.opengroup.org/onlinepubs/009695399/functions/malloc.html) and [`free()`](https://en.wikipedia.org/wi...
0
data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/language_overview/index.md
--- title: JavaScript language overview slug: Web/JavaScript/Language_overview page-type: guide --- {{jsSidebar}} JavaScript is a multi-paradigm, dynamic language with types and operators, standard built-in objects, and methods. Its syntax is based on the Java and C languages β€” many structures from those languages ap...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/guide/index.md
--- title: JavaScript Guide slug: Web/JavaScript/Guide page-type: guide --- {{jsSidebar("JavaScript Guide")}} The JavaScript Guide shows you how to use [JavaScript](/en-US/docs/Web/JavaScript) and gives an overview of the language. If you need exhaustive information about a language feature, have a look at the [JavaS...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/loops_and_iteration/index.md
--- title: Loops and iteration slug: Web/JavaScript/Guide/Loops_and_iteration page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Control_flow_and_error_handling", "Web/JavaScript/Guide/Functions")}} Loops offer a quick and easy way to do something repeatedly. This chapter of t...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/working_with_objects/index.md
--- title: Working with objects slug: Web/JavaScript/Guide/Working_with_objects page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Keyed_collections", "Web/JavaScript/Guide/Using_classes")}} JavaScript is designed on a simple object-based paradigm. An object is a collection of...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/expressions_and_operators/index.md
--- title: Expressions and operators slug: Web/JavaScript/Guide/Expressions_and_operators page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Functions", "Web/JavaScript/Guide/Numbers_and_dates")}} This chapter describes JavaScript's expressions and operators, including assignm...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/iterators_and_generators/index.md
--- title: Iterators and generators slug: Web/JavaScript/Guide/Iterators_and_generators page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Typed_arrays", "Web/JavaScript/Guide/Meta_programming")}} Iterators and Generators bring the concept of iteration directly into the core l...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/using_promises/index.md
--- title: Using promises slug: Web/JavaScript/Guide/Using_promises page-type: guide --- {{jsSidebar("JavaScript Guide")}}{{PreviousNext("Web/JavaScript/Guide/Using_classes", "Web/JavaScript/Guide/Typed_arrays")}} A {{jsxref("Promise")}} is an object representing the eventual completion or failure of an asynchronous ...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/text_formatting/index.md
--- title: Text formatting slug: Web/JavaScript/Guide/Text_formatting page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Numbers_and_dates", "Web/JavaScript/Guide/Regular_expressions")}} This chapter introduces how to work with strings and text in JavaScript. ## Strings Java...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/modules/index.md
--- title: JavaScript modules slug: Web/JavaScript/Guide/Modules page-type: guide browser-compat: - javascript.statements.import - javascript.statements.export --- {{jsSidebar("JavaScript Guide")}}{{Previous("Web/JavaScript/Guide/Meta_programming")}} This guide gives you all you need to get started with JavaScrip...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/control_flow_and_error_handling/index.md
--- title: Control flow and error handling slug: Web/JavaScript/Guide/Control_flow_and_error_handling page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Grammar_and_types", "Web/JavaScript/Guide/Loops_and_iteration")}} JavaScript supports a compact set of statements, specifica...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/indexed_collections/index.md
--- title: Indexed collections slug: Web/JavaScript/Guide/Indexed_collections page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Regular_expressions", "Web/JavaScript/Guide/Keyed_collections")}} This chapter introduces collections of data which are ordered by an index value. T...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/using_classes/index.md
--- title: Using classes slug: Web/JavaScript/Guide/Using_classes page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Working_with_objects", "Web/JavaScript/Guide/Using_promises")}} JavaScript is a prototype-based language β€” an object's behaviors are specified by its own proper...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/index.md
--- title: Regular expressions slug: Web/JavaScript/Guide/Regular_expressions page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Text_formatting", "Web/JavaScript/Guide/Indexed_collections")}} Regular expressions are patterns used to match character combinations in strings. In...
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data/mdn-content/files/en-us/web/javascript/guide/regular_expressions
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/character_classes/index.md
--- title: Character classes slug: Web/JavaScript/Guide/Regular_expressions/Character_classes page-type: guide --- {{jsSidebar("JavaScript Guide")}} Character classes distinguish kinds of characters such as, for example, distinguishing between letters and digits. {{EmbedInteractiveExample("pages/js/regexp-character-...
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data/mdn-content/files/en-us/web/javascript/guide/regular_expressions
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/cheatsheet/index.md
--- title: Regular expression syntax cheat sheet slug: Web/JavaScript/Guide/Regular_expressions/Cheatsheet page-type: guide --- {{jsSidebar("JavaScript Guide")}} This page provides an overall cheat sheet of all the capabilities of `RegExp` syntax by aggregating the content of the articles in the `RegExp` guide. If yo...
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data/mdn-content/files/en-us/web/javascript/guide/regular_expressions
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/groups_and_backreferences/index.md
--- title: Groups and backreferences slug: Web/JavaScript/Guide/Regular_expressions/Groups_and_backreferences page-type: guide --- {{jsSidebar("JavaScript Guide")}} Groups group multiple patterns as a whole, and capturing groups provide extra submatch information when using a regular expression pattern to match again...
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data/mdn-content/files/en-us/web/javascript/guide/regular_expressions
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/assertions/index.md
--- title: Assertions slug: Web/JavaScript/Guide/Regular_expressions/Assertions page-type: guide --- {{jsSidebar("JavaScript Guide")}} Assertions include boundaries, which indicate the beginnings and endings of lines and words, and other patterns indicating in some way that a match is possible (including look-ahead, ...
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data/mdn-content/files/en-us/web/javascript/guide/regular_expressions
data/mdn-content/files/en-us/web/javascript/guide/regular_expressions/quantifiers/index.md
--- title: Quantifiers slug: Web/JavaScript/Guide/Regular_expressions/Quantifiers page-type: guide --- {{jsSidebar("JavaScript Guide")}} Quantifiers indicate numbers of characters or expressions to match. {{EmbedInteractiveExample("pages/js/regexp-quantifiers.html", "taller")}} ## Types > **Note:** In the followin...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/functions/index.md
--- title: Functions slug: Web/JavaScript/Guide/Functions page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Loops_and_iteration", "Web/JavaScript/Guide/Expressions_and_operators")}} Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript i...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/numbers_and_dates/index.md
--- title: Numbers and dates slug: Web/JavaScript/Guide/Numbers_and_dates page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Expressions_and_operators", "Web/JavaScript/Guide/Text_formatting")}} This chapter introduces the concepts, objects and functions used to work with and ...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/typed_arrays/index.md
--- title: JavaScript typed arrays slug: Web/JavaScript/Guide/Typed_arrays page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Using_promises", "Web/JavaScript/Guide/Iterators_and_generators")}} JavaScript typed arrays are array-like objects that provide a mechanism for reading...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/meta_programming/index.md
--- title: Meta programming slug: Web/JavaScript/Guide/Meta_programming page-type: guide --- {{jsSidebar("JavaScript Guide")}}{{PreviousNext("Web/JavaScript/Guide/Iterators_and_generators", "Web/JavaScript/Guide/Modules")}} The {{jsxref("Proxy")}} and {{jsxref("Reflect")}} objects allow you to intercept and define cu...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/grammar_and_types/index.md
--- title: Grammar and types slug: Web/JavaScript/Guide/Grammar_and_types page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Introduction", "Web/JavaScript/Guide/Control_flow_and_error_handling")}} This chapter discusses JavaScript's basic grammar, variable declarations, data ...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/introduction/index.md
--- title: Introduction slug: Web/JavaScript/Guide/Introduction page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide", "Web/JavaScript/Guide/Grammar_and_types")}} This chapter introduces JavaScript and discusses some of its fundamental concepts. ## What you should already know ...
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data/mdn-content/files/en-us/web/javascript/guide
data/mdn-content/files/en-us/web/javascript/guide/keyed_collections/index.md
--- title: Keyed collections slug: Web/JavaScript/Guide/Keyed_collections page-type: guide --- {{jsSidebar("JavaScript Guide")}} {{PreviousNext("Web/JavaScript/Guide/Indexed_collections", "Web/JavaScript/Guide/Working_with_objects")}} This chapter introduces collections of data which are indexed by a key; `Map` and `...
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data/mdn-content/files/en-us/web/javascript
data/mdn-content/files/en-us/web/javascript/reference/index.md
--- title: JavaScript reference slug: Web/JavaScript/Reference page-type: landing-page --- {{jsSidebar}} The JavaScript reference serves as a repository of facts about the JavaScript language. The entire language is described here in detail. As you write JavaScript code, you'll refer to these pages often (thus the ti...
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data/mdn-content/files/en-us/web/javascript/reference
data/mdn-content/files/en-us/web/javascript/reference/trailing_commas/index.md
--- title: Trailing commas slug: Web/JavaScript/Reference/Trailing_commas page-type: javascript-language-feature browser-compat: javascript.grammar.trailing_commas --- {{jsSidebar("More")}} **Trailing commas** (sometimes called "final commas") can be useful when adding new elements, parameters, or properties to JavaS...
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data/mdn-content/files/en-us/web/javascript/reference
data/mdn-content/files/en-us/web/javascript/reference/strict_mode/index.md
--- title: Strict mode slug: Web/JavaScript/Reference/Strict_mode page-type: guide spec-urls: https://tc39.es/ecma262/multipage/strict-mode-of-ecmascript.html --- {{jsSidebar("More")}} > **Note:** Sometimes you'll see the default, non-strict mode referred to as _[sloppy mode](/en-US/docs/Glossary/Sloppy_mode)_. This ...
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data/mdn-content/files/en-us/web/javascript/reference
data/mdn-content/files/en-us/web/javascript/reference/classes/index.md
--- title: Classes slug: Web/JavaScript/Reference/Classes page-type: guide browser-compat: javascript.classes --- {{jsSidebar("Classes")}} Classes are a template for creating objects. They encapsulate data with code to work on that data. Classes in JS are built on [prototypes](/en-US/docs/Web/JavaScript/Inheritance_a...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/public_class_fields/index.md
--- title: Public class fields slug: Web/JavaScript/Reference/Classes/Public_class_fields page-type: javascript-language-feature browser-compat: javascript.classes.public_class_fields --- {{jsSidebar("Classes")}} **Public fields** are writable, enumerable, and configurable properties. As such, unlike their private co...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/static_initialization_blocks/index.md
--- title: Static initialization blocks slug: Web/JavaScript/Reference/Classes/Static_initialization_blocks page-type: javascript-language-feature browser-compat: javascript.classes.static_initialization_blocks --- {{jsSidebar("Classes")}} **Static initialization blocks** are declared within a {{jsxref("Statements/cl...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/extends/index.md
--- title: extends slug: Web/JavaScript/Reference/Classes/extends page-type: javascript-language-feature browser-compat: javascript.classes.extends --- {{jsSidebar("Classes")}} The **`extends`** keyword is used in [class declarations](/en-US/docs/Web/JavaScript/Reference/Statements/class) or [class expressions](/en-U...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/static/index.md
--- title: static slug: Web/JavaScript/Reference/Classes/static page-type: javascript-language-feature browser-compat: javascript.classes.static --- {{jsSidebar("Classes")}} The **`static`** keyword defines a [static method or field](/en-US/docs/Web/JavaScript/Reference/Classes#static_methods_and_fields) for a class,...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/constructor/index.md
--- title: constructor slug: Web/JavaScript/Reference/Classes/constructor page-type: javascript-language-feature browser-compat: javascript.classes.constructor --- {{jsSidebar("Classes")}} The **`constructor`** method is a special method of a [class](/en-US/docs/Web/JavaScript/Reference/Classes) for creating and init...
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data/mdn-content/files/en-us/web/javascript/reference/classes
data/mdn-content/files/en-us/web/javascript/reference/classes/private_properties/index.md
--- title: Private properties slug: Web/JavaScript/Reference/Classes/Private_properties page-type: javascript-language-feature browser-compat: - javascript.classes.private_class_fields - javascript.classes.private_class_fields_in - javascript.classes.private_class_methods --- {{jsSidebar("Classes")}} **Private ...
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data/mdn-content/files/en-us/web/javascript/reference
data/mdn-content/files/en-us/web/javascript/reference/errors/index.md
--- title: JavaScript error reference slug: Web/JavaScript/Reference/Errors page-type: landing-page --- {{jsSidebar("Errors")}} Below, you'll find a list of errors which are thrown by JavaScript. These errors can be a helpful debugging aid, but the reported problem isn't always immediately clear. The pages below will...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/unexpected_token/index.md
--- title: "SyntaxError: Unexpected token" slug: Web/JavaScript/Reference/Errors/Unexpected_token page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exceptions "unexpected token" occur when a specific language construct was expected, but something else was provided. This might be a simple typo. #...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_const_assignment/index.md
--- title: 'TypeError: invalid assignment to const "x"' slug: Web/JavaScript/Reference/Errors/Invalid_const_assignment page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "invalid assignment to const" occurs when it was attempted to alter a constant value. JavaScript [`const`](/en-US/docs...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/already_has_pragma/index.md
--- title: "Warning: -file- is being assigned a //# sourceMappingURL, but already has one" slug: Web/JavaScript/Reference/Errors/Already_has_pragma page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript warning "-file- is being assigned a //# sourceMappingURL, but already has one." occurs when a sourc...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/json_bad_parse/index.md
--- title: "SyntaxError: JSON.parse: bad parsing" slug: Web/JavaScript/Reference/Errors/JSON_bad_parse page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exceptions thrown by {{jsxref("JSON.parse()")}} occur when string failed to be parsed as JSON. ## Message ```plain SyntaxError: JSON.parse: un...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/delete_in_strict_mode/index.md
--- title: "SyntaxError: applying the 'delete' operator to an unqualified name is deprecated" slug: Web/JavaScript/Reference/Errors/Delete_in_strict_mode page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript [strict mode](/en-US/docs/Web/JavaScript/Reference/Strict_mode)-only exception "applying the ...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_for-in_initializer/index.md
--- title: "SyntaxError: for-in loop head declarations may not have initializers" slug: Web/JavaScript/Reference/Errors/Invalid_for-in_initializer page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript [strict mode](/en-US/docs/Web/JavaScript/Reference/Strict_mode)-only exception "for-in loop head dec...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/in_operator_no_object/index.md
--- title: "TypeError: cannot use 'in' operator to search for 'x' in 'y'" slug: Web/JavaScript/Reference/Errors/in_operator_no_object page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "right-hand side of 'in' should be an object" occurs when the [`in` operator](/en-US/docs/Web/JavaScrip...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_initializer_in_const/index.md
--- title: "SyntaxError: missing = in const declaration" slug: Web/JavaScript/Reference/Errors/Missing_initializer_in_const page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing = in const declaration" occurs when a const declaration was not given a value in the same statement (lik...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cant_assign_to_property/index.md
--- title: 'TypeError: can''t assign to property "x" on "y": not an object' slug: Web/JavaScript/Reference/Errors/Cant_assign_to_property page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript strict mode exception "can't assign to property" occurs when attempting to create a property on [primitive](/...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/called_on_incompatible_type/index.md
--- title: "TypeError: X.prototype.y called on incompatible type" slug: Web/JavaScript/Reference/Errors/Called_on_incompatible_type page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "called on incompatible target (or object)" occurs when a function (on a given object), is called with a ...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_curly_after_function_body/index.md
--- title: "SyntaxError: missing } after function body" slug: Web/JavaScript/Reference/Errors/Missing_curly_after_function_body page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing } after function body" occurs when there is a syntax mistake when creating a function somewhere. Che...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/getter_only/index.md
--- title: 'TypeError: setting getter-only property "x"' slug: Web/JavaScript/Reference/Errors/Getter_only page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript [strict mode](/en-US/docs/Web/JavaScript/Reference/Strict_mode)-only exception "setting getter-only property" occurs when there is an attemp...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/bad_return/index.md
--- title: "SyntaxError: return not in function" slug: Web/JavaScript/Reference/Errors/Bad_return page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "return not in function" occurs when a [`return`](/en-US/docs/Web/JavaScript/Reference/Statements/return) statement is called outside of a ...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/resulting_string_too_large/index.md
--- title: "RangeError: repeat count must be less than infinity" slug: Web/JavaScript/Reference/Errors/Resulting_string_too_large page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "repeat count must be less than infinity" occurs when the {{jsxref("String.prototype.repeat()")}} method is...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cant_define_property_object_not_extensible/index.md
--- title: 'TypeError: can''t define property "x": "obj" is not extensible' slug: Web/JavaScript/Reference/Errors/Cant_define_property_object_not_extensible page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "can't define property "x": "obj" is not extensible" occurs when {{jsxref("Objec...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_for-of_initializer/index.md
--- title: "SyntaxError: a declaration in the head of a for-of loop can't have an initializer" slug: Web/JavaScript/Reference/Errors/Invalid_for-of_initializer page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "a declaration in the head of a for-of loop can't have an initializer" occurs...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cant_use_nullish_coalescing_unparenthesized/index.md
--- title: "SyntaxError: cannot use `??` unparenthesized within `||` and `&&` expressions" slug: Web/JavaScript/Reference/Errors/Cant_use_nullish_coalescing_unparenthesized page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "cannot use `??` unparenthesized within `||` and `&&` expression...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_parenthesis_after_condition/index.md
--- title: "SyntaxError: missing ) after condition" slug: Web/JavaScript/Reference/Errors/Missing_parenthesis_after_condition page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing ) after condition" occurs when there is an error with how an [`if`](/en-US/docs/Web/JavaScript/Referen...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_assignment_left-hand_side/index.md
--- title: "SyntaxError: invalid assignment left-hand side" slug: Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "invalid assignment left-hand side" occurs when there was an unexpected assignment somewhere. It may be t...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/unexpected_type/index.md
--- title: 'TypeError: "x" is (not) "y"' slug: Web/JavaScript/Reference/Errors/Unexpected_type page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "_x_ is (not) _y_" occurs when there was an unexpected type. Oftentimes, unexpected {{jsxref("undefined")}} or [`null`](/en-US/docs/Web/JavaSc...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_right_hand_side_instanceof_operand/index.md
--- title: "TypeError: invalid 'instanceof' operand 'x'" slug: Web/JavaScript/Reference/Errors/invalid_right_hand_side_instanceof_operand page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "invalid 'instanceof' operand" occurs when the right-hand side operands of the [`instanceof` operat...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/deprecated_source_map_pragma/index.md
--- title: "SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead" slug: Web/JavaScript/Reference/Errors/Deprecated_source_map_pragma page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript warning "Using `//@` to indicate sourceURL pragmas is deprecated. Use `//#` instead...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/equal_as_assign/index.md
--- title: "SyntaxError: test for equality (==) mistyped as assignment (=)?" slug: Web/JavaScript/Reference/Errors/Equal_as_assign page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript warning "test for equality (==) mistyped as assignment (=)?" occurs when there was an assignment (`=`) when you woul...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/not_defined/index.md
--- title: 'ReferenceError: "x" is not defined' slug: Web/JavaScript/Reference/Errors/Not_defined page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "_variable_ is not defined" occurs when there is a non-existent variable referenced somewhere. ## Message ```plain ReferenceError: "x" is...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/either_be_both_static_or_non-static/index.md
--- title: "SyntaxError: getter and setter for private name #x should either be both static or non-static" slug: Web/JavaScript/Reference/Errors/Either_be_both_static_or_non-static page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "mismatched placement" occurs when a private [getter](/e...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_bigint_syntax/index.md
--- title: "SyntaxError: invalid BigInt syntax" slug: Web/JavaScript/Reference/Errors/Invalid_BigInt_syntax page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "invalid BigInt syntax" occurs when a string value is being coerced to a {{jsxref("BigInt")}} but it failed to be parsed as an in...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/stmt_after_return/index.md
--- title: "Warning: unreachable code after return statement" slug: Web/JavaScript/Reference/Errors/Stmt_after_return page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript warning "unreachable code after return statement" occurs when using an expression after a {{jsxref("Statements/return", "return")...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/no_properties/index.md
--- title: 'TypeError: "x" has no properties' slug: Web/JavaScript/Reference/Errors/No_properties page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "null (or undefined) has no properties" occurs when you attempt to access properties of [`null`](/en-US/docs/Web/JavaScript/Reference/Opera...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cyclic_prototype/index.md
--- title: "TypeError: can't set prototype: it would cause a prototype chain cycle" slug: Web/JavaScript/Reference/Errors/Cyclic_prototype page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "TypeError: can't set prototype: it would cause a prototype chain cycle" occurs when an object's p...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cant_access_lexical_declaration_before_init/index.md
--- title: "ReferenceError: can't access lexical declaration 'X' before initialization" slug: Web/JavaScript/Reference/Errors/Cant_access_lexical_declaration_before_init page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "can't access lexical declaration \`_variable_' before initializati...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_bracket_after_list/index.md
--- title: "SyntaxError: missing ] after element list" slug: Web/JavaScript/Reference/Errors/Missing_bracket_after_list page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing ] after element list" occurs when there is an error with the array initializer syntax somewhere. Likely ther...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/no_non-null_object/index.md
--- title: 'TypeError: "x" is not a non-null object' slug: Web/JavaScript/Reference/Errors/No_non-null_object page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "is not a non-null object" occurs when an object is expected somewhere and wasn't provided. [`null`](/en-US/docs/Web/JavaScript...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/unnamed_function_statement/index.md
--- title: "SyntaxError: function statement requires a name" slug: Web/JavaScript/Reference/Errors/Unnamed_function_statement page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "function statement requires a name" occurs when there is a [function statement](/en-US/docs/Web/JavaScript/Ref...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/bigint_negative_exponent/index.md
--- title: "RangeError: BigInt negative exponent" slug: Web/JavaScript/Reference/Errors/BigInt_negative_exponent page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "BigInt negative exponent" occurs when a {{jsxref("BigInt")}} is raised to the power of a negative BigInt value. ## Message...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/more_arguments_needed/index.md
--- title: "TypeError: More arguments needed" slug: Web/JavaScript/Reference/Errors/More_arguments_needed page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "more arguments needed" occurs when there is an error with how a function is called. More arguments need to be provided. ## Messag...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/identifier_after_number/index.md
--- title: "SyntaxError: identifier starts immediately after numeric literal" slug: Web/JavaScript/Reference/Errors/Identifier_after_number page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "identifier starts immediately after numeric literal" occurs when an identifier started with a di...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_curly_after_property_list/index.md
--- title: "SyntaxError: missing } after property list" slug: Web/JavaScript/Reference/Errors/Missing_curly_after_property_list page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing } after property list" occurs when there is a mistake in the [object initializer](/en-US/docs/Web/Ja...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/missing_colon_after_property_id/index.md
--- title: "SyntaxError: missing : after property id" slug: Web/JavaScript/Reference/Errors/Missing_colon_after_property_id page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "missing : after property id" occurs when objects are created using the [object initializer](/en-US/docs/Web/Java...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/label_not_found/index.md
--- title: "SyntaxError: label not found" slug: Web/JavaScript/Reference/Errors/Label_not_found page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "label not found" occurs when a {{jsxref("Statements/break", "break")}} or {{jsxref("Statements/continue", "continue")}} statement references...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/invalid_array_length/index.md
--- title: "RangeError: invalid array length" slug: Web/JavaScript/Reference/Errors/Invalid_array_length page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "Invalid array length" occurs when specifying an array length that is either negative, a floating number or exceeds the maximum supp...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cant_convert_x_to_bigint/index.md
--- title: "TypeError: can't convert x to BigInt" slug: Web/JavaScript/Reference/Errors/Cant_convert_x_to_BigInt page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "x can't be converted to BigInt" occurs when attempting to convert a {{jsxref("Symbol")}}, [`null`](/en-US/docs/Web/JavaScri...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/bad_radix/index.md
--- title: "RangeError: radix must be an integer" slug: Web/JavaScript/Reference/Errors/Bad_radix page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "radix must be an integer at least 2 and no greater than 36" occurs when the optional `radix` parameter of the {{jsxref("Number.prototype.t...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/undeclared_var/index.md
--- title: 'ReferenceError: assignment to undeclared variable "x"' slug: Web/JavaScript/Reference/Errors/Undeclared_var page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript [strict mode](/en-US/docs/Web/JavaScript/Reference/Strict_mode)-only exception "Assignment to undeclared variable" occurs when ...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/cyclic_object_value/index.md
--- title: "TypeError: cyclic object value" slug: Web/JavaScript/Reference/Errors/Cyclic_object_value page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "cyclic object value" occurs when object references were found in [JSON](https://www.json.org/). {{jsxref("JSON.stringify()")}} doesn't...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/unparenthesized_unary_expr_lhs_exponentiation/index.md
--- title: "SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'" slug: Web/JavaScript/Reference/Errors/Unparenthesized_unary_expr_lhs_exponentiation page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "unparenthesized unary expression can't appear on t...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/malformed_uri/index.md
--- title: "URIError: malformed URI sequence" slug: Web/JavaScript/Reference/Errors/Malformed_URI page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "malformed URI sequence" occurs when URI encoding or decoding wasn't successful. ## Message ```plain URIError: URI malformed (V8-based) U...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/read-only/index.md
--- title: 'TypeError: "x" is read-only' slug: Web/JavaScript/Reference/Errors/Read-only page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript [strict mode](/en-US/docs/Web/JavaScript/Reference/Strict_mode)-only exception "is read-only" occurs when a global variable or object property that was assign...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/not_a_constructor/index.md
--- title: 'TypeError: "x" is not a constructor' slug: Web/JavaScript/Reference/Errors/Not_a_constructor page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "is not a constructor" occurs when there was an attempt to use an object or a variable as a constructor, but that object or variable...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/too_much_recursion/index.md
--- title: "InternalError: too much recursion" slug: Web/JavaScript/Reference/Errors/Too_much_recursion page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "too much recursion" or "Maximum call stack size exceeded" occurs when there are too many function calls, or a function is missing a ...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/strict_non_simple_params/index.md
--- title: 'SyntaxError: "use strict" not allowed in function with non-simple parameters' slug: Web/JavaScript/Reference/Errors/Strict_non_simple_params page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript exception "`"use strict"` not allowed in function" occurs when a `"use strict"` directive is u...
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data/mdn-content/files/en-us/web/javascript/reference/errors
data/mdn-content/files/en-us/web/javascript/reference/errors/undefined_prop/index.md
--- title: 'ReferenceError: reference to undefined property "x"' slug: Web/JavaScript/Reference/Errors/Undefined_prop page-type: javascript-error --- {{jsSidebar("Errors")}} The JavaScript warning "reference to undefined property" occurs when a script attempted to access an object property which doesn't exist. ## Me...
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