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TypeScript (abbreviated as TS) is a high-level
programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
that adds static typing with optional type annotations to
JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...
. It is designed for developing large applications and transpiles to JavaScript. It is developed by
Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...
as
free and open-source software Free and open-source software (FOSS) is software available under a license that grants users the right to use, modify, and distribute the software modified or not to everyone free of charge. FOSS is an inclusive umbrella term encompassing free ...
released under an Apache License 2.0. TypeScript may be used to develop JavaScript applications for both client-side and server-side execution (as with Node.js, Deno or Bun). Multiple options are available for transpiling. The default TypeScript Compiler can be used, or the Babel compiler can be invoked to convert TypeScript to JavaScript. TypeScript supports definition files that can contain type information of existing JavaScript libraries, much like C++ header files can describe the structure of existing object files. This enables other programs to use the values defined in the files as if they were statically typed TypeScript entities. There are third-party header files for popular libraries such as jQuery, MongoDB, and D3.js. TypeScript headers for the Node.js library modules are also available, allowing development of Node.js programs within TypeScript. The TypeScript compiler is written in TypeScript and compiled to JavaScript. It is licensed under the Apache License 2.0. Anders Hejlsberg, lead architect of C# and creator of
Delphi Delphi (; ), in legend previously called Pytho (Πυθώ), was an ancient sacred precinct and the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient Classical antiquity, classical world. The A ...
and Turbo Pascal, has worked on developing TypeScript.


History

TypeScript was released to the public in October 2012, with version 0.8, after two years of internal development at Microsoft. Soon after the initial public release, Miguel de Icaza praised the language, but criticized the lack of mature
integrated development environment An integrated development environment (IDE) is a Application software, software application that provides comprehensive facilities for software development. An IDE normally consists of at least a source-code editor, build automation tools, an ...
(IDE) support apart from Microsoft Visual Studio, which was unavailable then on
Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
and
macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...
. As of April 2021 there is support in other IDEs and text editors, including Emacs, Vim, WebStorm,
Atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
and Microsoft's own Visual Studio Code. TypeScript 0.9, released in 2013, added support for generics. TypeScript 1.0 was released at Microsoft's Build developer conference in 2014. Visual Studio 2013 Update 2 provided built-in support for TypeScript. Further improvement were made in July 2014, when the development team announced a new TypeScript compiler, asserted to have a five-fold performance increase. Simultaneously, the source code, which was initially hosted on CodePlex, was moved to
GitHub GitHub () is a Proprietary software, proprietary developer platform that allows developers to create, store, manage, and share their code. It uses Git to provide distributed version control and GitHub itself provides access control, bug trackin ...
. On 22 September 2016, TypeScript 2.0 was released, introducing several features, including the ability for programmers to optionally enforce null safety, to mitigate what's sometimes referred to as the billion-dollar mistake. TypeScript 3.0 was released on 30 July 2018, bringing many language additions like tuples in rest parameters and spread expressions, rest parameters with tuple types, generic rest parameters and so on. TypeScript 4.0 was released on 20 August 2020. While 4.0 did not introduce any breaking changes, it added language features such as Custom JSX Factories and Variadic Tuple Types. TypeScript 5.0 was released on 16 March 2023 and included support for decorators. On March 11, 2025 Anders Hejlsberg announced on the TypeScript blog that the team is working on a Go port of the TypeScript compiler to be released as TypeScript version 7.0 later this year. It is expected to feature a 10x speedup.


Design

TypeScript originated from the shortcomings of JavaScript for developing large-scale applications both at Microsoft and among their external customers. Challenges with dealing with complex JavaScript code led to demand for custom tooling to ease developing of components in the language. Developers sought a solution that would not break compatibility with the
ECMAScript ECMAScript (; ES) is a standard for scripting languages, including JavaScript, JScript, and ActionScript. It is best known as a JavaScript standard intended to ensure the interoperability of web pages across different web browsers. It is stan ...
(ES) standard and its ecosystem, so a
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...
was developed to transform a superset of JavaScript with type annotations and classes (TypeScript files) back into vanilla ECMAScript 5 code. TypeScript classes were based on the then-proposed ECMAScript 6 class specification to make writing prototypal inheritance less verbose and error-prone, and type annotations enabled IntelliSense and improved tooling.


Features

TypeScript adds the following syntax extensions to JavaScript: * Type signatures (annotations) and compile-time type checking * Type inference * Interfaces *
Enumerated type In computer programming, an enumerated type (also called enumeration, enum, or factor in the R (programming language), R programming language, a status variable in the JOVIAL programming language, and a categorical variable in statistics) is a data ...
s * Generics *
Namespace In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...
s *
Tuple In mathematics, a tuple is a finite sequence or ''ordered list'' of numbers or, more generally, mathematical objects, which are called the ''elements'' of the tuple. An -tuple is a tuple of elements, where is a non-negative integer. There is o ...
s * Explicit resource management Syntactically, TypeScript is very similar to JScript .NET, another Microsoft implementation of the ECMA-262 language standard that added support for static typing and classical object-oriented language features such as classes, inheritance, interfaces, and namespaces. Other inspirations include
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and C#.


Type annotations

TypeScript provides static typing through type annotations to enable type checking at compile time. function add(left: number, right: number): number Primitive types are annotated using all-lowercase types, such as number, boolean, bigint, and string. These types are distinct from their boxed counterparts (Number, Boolean, etc), which cannot have operations performed from values directly (a Number and number cannot be added). There are additionally undefined and null types for their respective values. All other non-primitive types are annotated using their class name, such as Error. Arrays can be written in two different ways which are both syntactically the same: the generic-based syntax Array and a shorthand with T[]. Additional built-in data types are tuples, unions, never and any: * An array with predefined data types at each index is a tuple, represented as [type1, type2, ..., typeN]. * A variable that can hold more than one type of data is a union, represented using the logical OR , symbol (string , number). * The never type is used when a given type should be impossible to create, which is useful for filtering mapped types. * A value of type any supports the same operations as a value in JavaScript and minimal static type checking is performed, which makes it suitable for weakly or dynamically-typed structures. This is generally discouraged practice and should be avoided when possible. Type annotations can be exported to a separate ''declarations file'' to make type information available for TypeScript scripts using types already compiled into JavaScript. Annotations can be declared for an existing JavaScript library, as has been done for Node.js and jQuery. The TypeScript compiler makes use of type inference when types are not given. For example, the add method in the code above would be inferred as returning a number even if no return type annotation had been provided. This is based on the static types of left and right being numbers, and the compiler's knowledge that the result of adding two numbers is always a number. If no type can be inferred because of lack of declarations (such as in a JavaScript module without types), then it defaults to the dynamic any type. Additional module types can be provided using a .d.ts declaration file using the declare module "moduleName" syntax.


Declaration files

When a TypeScript script gets compiled, there is an option to generate a ''declaration file'' (with the extension .d.ts) that functions as an interface to the components in the compiled JavaScript. In the process, the compiler strips away all function and method bodies and preserves only the signatures of the types that are exported. The resulting declaration file can then be used to describe the exported virtual TypeScript types of a JavaScript library or module when a third-party developer consumes it from TypeScript. The concept of declaration files is analogous to the concept of header files found in C/C++. declare namespace Arithmetics Type declaration files can be written by hand for existing JavaScript libraries, as has been done for jQuery and Node.js. Large collections of declaration files for popular JavaScript libraries are hosted on GitHub i
DefinitelyTyped


Generics

TypeScript supports generic programming using a syntax similar to
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. The following is an example of the identity function. function id(x: T): T


Classes

TypeScript uses the same annotation style for class methods and fields as for functions and variables respectively. Compared with vanilla JavaScript classes, a TypeScript class can also implement an interface through the implements keyword, use generic parameters similarly to
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
, and specify public and private fields. class Person


Union types


Enumerated types


Modules and namespaces

TypeScript distinguishes between modules and namespaces. Both features in TypeScript support encapsulation of classes, interfaces, functions and variables into containers. Namespaces (formerly internal modules) use JavaScript immediately-invoked function expressions to encapsulate code, whereas modules (formerly external modules) use existing JavaScript library patterns ( CommonJS or ES Modules).


Compatibility with JavaScript

As TypeScript is simply a superset of JavaScript, existing JavaScript can be quickly adapted to TypeScript and TypeScript program can seamlessly consume JavaScript. The compiler can target all ECMAScript versions 5 and above, transpiling modern features like classes and arrow functions to their older counterparts. With TypeScript, it is possible to use existing JavaScript code, incorporate popular JavaScript libraries, and call TypeScript-generated code from other JavaScript. Type declarations for these libraries are usually provided with the source code but can be declared or installed separately if needed.


Development tools


Compiler

The TypeScript compiler, named tsc, is written in TypeScript. As a result, it can be compiled into regular JavaScript and can then be executed in any JavaScript engine (e.g. a browser). The compiler package comes bundled with a script host that can execute the compiler. It is also available as a Node.js package that uses Node.js as a host. The compiler can ''target'' a given edition of ECMAScript (such as ECMAScript 5 for legacy browser compatibility), but by default compiles for the latest standards.


IDE and editor support

*
Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...
provides a plug-in for Visual Studio 2012 and WebMatrix, full integrated support in Visual Studio 2013, Visual Studio 2015, and basic text editor support for Emacs and Vim. * Visual Studio Code supports TypeScript in addition to several other languages, and offers features like debugging and intelligent code completion. * alm.tools is an open source cloud IDE for TypeScript built using TypeScript, ReactJS and TypeStyle. * JetBrains supports TypeScript with code completion, refactoring and debugging in its IDEs built on IntelliJ platform, such as
PhpStorm JetBrains s.r.o. (formerly IntelliJ Software s.r.o.) is a Czech software development private limited company which makes tools for software developers and project managers. The company has its headquarters in Amsterdam, and has offices in Ch ...
6, WebStorm 6, and IntelliJ IDEA, as well as their Visual Studio Add-in and extension, ReSharper 8.1. *
Atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
has a TypeScript plugin with support for code completion, navigation, formatting, and fast compilation. * The online Cloud9 IDE and Codenvy support TypeScript. * A plugin is available for the
NetBeans NetBeans is an integrated development environment (IDE) for Java (programming language), Java. NetBeans allows applications to be developed from a set of modular software components called ''modules''. NetBeans runs on Microsoft Windows, Windows, ...
IDE. * A plugin is available for the Eclipse IDE (version Kepler) * TypEcs is available for the Eclipse IDE. * The Cross Platform Cloud IDE Codeanywhere supports TypeScript. * Webclipse An Eclipse plugin designed to develop TypeScript and Angular 2. * Angular IDE A standalone IDE available via npm to develop TypeScript and Angular 2 applications, with integrated terminal support. * Tide TypeScript Interactive Development Environment for Emacs.


Integration with build automation tools

Using plug-ins, TypeScript can be integrated with build automation tools, including Grunt (grunt-ts), Apache Maven (TypeScript Maven Plugin), Gulp (gulp-typescript) and Gradle (TypeScript Gradle Plugin).


Linting tools

TSLint scans TypeScript code for conformance to a set of standards and guidelines. ESLint, a standard JavaScript linter, also provided some support for TypeScript via community plugins. However, ESLint's inability to leverage TypeScript's language services precluded certain forms of semantic linting and program-wide analysis. In early 2019, the TSLint team announced the linter's deprecation in favor of typescript-eslint, a joint effort of the TSLint, ESLint and TypeScript teams to consolidate linting under the ESLint umbrella for improved performance, community unity and developer accessibility.


Release history


See also

* Dart * Kotlin *
JS++ JS++ is a programming language for web development that extends JavaScript with a sound type system. It includes imperative, object-oriented, functional, and generic programming features. It is free and open-source software released under ...
* PureScript


References


Citations


Sources


"Webclipse: Eclipse Plugin"
Genuitec. Retrieved 9 November 2016.
"Angular IDE by Webclipse: Standalone IDE"
Genuitec. Retrieved 9 November 2016.


External links

* * {{Authority control 2012 software Cross-platform software JavaScript programming language family Microsoft free software Microsoft programming languages Object-based programming languages Programming languages created in 2012 Programming languages Scripting languages Software using the Apache license Source-to-source compilers Statically typed programming languages Articles with example JavaScript code