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
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
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
number
s, and the compiler's knowledge that the result of adding two
number
s 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
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 ...
. 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