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{{Infobox programming language
 | name                   = TypeScript
 | logo                   = [[File:TypeScript Logo.png|frameless]]
 | logo caption           = 
 | screenshot             = 
 | screenshot caption     = 
 | file ext               = .ts
 | paradigm               = [[Multi-paradigm programming language|Multi-paradigm]]: [[scripting language|scripting]], [[object-oriented programming|object-oriented]], [[structured programming|structured]], [[imperative programming|imperative]], [[functional programming|functional]], [[generic programming|generic]]
 | scope                  =
 | released               = {{Start date|2012|10|1}}<ref>{{cite web | url=https://typescript.codeplex.com/releases/view/95554 | title=TypeScript | work=[[CodePlex]] | accessdate=26 April 2015}}</ref>
 | designer               = [[Microsoft]]
 | developer              = [[Microsoft]]
 | latest release version = 1.8
 | latest release date    =January, 2016 
 | latest preview version = 
 | latest preview date    = 
 | typing                 = 
 | implementations        = 
 | dialects               = 
 | influenced by          = [[JavaScript]], [[Java (programming language)|Java]], [[C Sharp (programming language)|C#]]
 | influenced             = [[AtScript]]
 | programming language   = 
 | platform               = 
 | operating system       = 
 | license                = [[Apache License| Apache License 2.0 ]]
 | website                = {{URL|https://www.typescriptlang.org/}}
 | wikibooks              = 
}}
'''TypeScript''' is a [[free and open source]] programming language developed and maintained by [[Microsoft]]. It is a strict [[superset]] of [[JavaScript]], and adds optional static typing and class-based [[object-oriented programming]] to the language. [[Anders Hejlsberg]], lead architect of [[C Sharp (programming language)#|C#]] and creator of [[Delphi programming language|Delphi]] and [[Turbo Pascal]], has worked on the development of TypeScript.<ref>{{cite web |url=https://www.zdnet.com/microsoft-takes-the-wraps-off-typescript-a-superset-of-javascript-7000004993/ |title=Microsoft takes the wraps off TypeScript, a superset of JavaScript |work=[[ZDNet]] |publisher=[[CBS Interactive]] |date=1 October 2012 |first=Mary Jo |last=Foley |accessdate=26 April 2015}}</ref><ref>{{cite web |url=https://blogs.msdn.com/b/somasegar/archive/2012/10/01/typescript-javascript-development-at-application-scale.aspx |title=Somasegar’s blog |date=1 October 2012 |publisher=Microsoft |work=Somasegar’s blog |first=S. |last=Somasegar |accessdate=26 April 2015}}</ref><ref>{{cite web|url=https://www.zdnet.com/microsoft-typescript-can-the-father-of-c-save-us-from-the-tyranny-of-javascript-7000005054/|title=Microsoft TypeScript: Can the father of C# save us from the tyranny of JavaScript?|first=Matt |last=Baxter-Reynolds|date=1 October 2012|work=[[ZDNet]]|accessdate=26 April 2015}}</ref><ref>{{cite web |url=https://www.cio.com/article/717679/Microsoft_Augments_Javascript_for_Large_scale_Development |title=Microsoft Augments Javascript for Large-scale Development |first=Joab |last=Jackson |date=1 October 2012 |work=CIO |publisher=[[IDG Enterprise]] |accessdate=26 April 2015}}</ref> TypeScript may be used to develop JavaScript applications for [[client-side]] or [[server-side]] ([[Node.js]]) execution.

TypeScript is designed for development of large applications and [[source-to-source compiler|transcompiles]] to JavaScript.<ref>{{cite web |url=https://arstechnica.com/information-technology/2012/10/microsoft-typescript-the-javascript-we-need-or-a-solution-looking-for-a-problem/ |title=Microsoft TypeScript: the JavaScript we need, or a solution looking for a problem? |first=Peter |last=Bright |date=3 October 2012 |work=[[Ars Technica]] |publisher=[[Condé Nast]] |accessdate=26 April 2015}}</ref> As TypeScript is a superset of JavaScript, any existing JavaScript programs are also valid TypeScript programs.

TypeScript supports definition files that can contain type information of existing JavaScript libraries, much like C/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 like [[jQuery]], [[MongoDB]], and [[D3.js]]. TypeScript headers for the [[Node.js]] basic modules are also available, allowing development of Node.js programs within TypeScript.<ref>{{cite web |url=https://github.com/borisyankov/DefinitelyTyped |title=borisyankov/DefinitelyTyped |date= |work=[[GitHub]] |accessdate=26 April 2015}}</ref>

The TypeScript compiler is itself written in TypeScript, [[Source-to-source compiler|transcompiled]] to JavaScript and licensed under the [[Apache 2 License]].

TypeScript is included as a first-class programming language in [[Microsoft Visual Studio]] 2013 Update 2 and later, beside [[C sharp (programming language)|C#]] and other Microsoft languages.<ref>[https://www.typescriptlang.org/ TypeScript Homepage], ''"Visual Studio includes TypeScript in the box, starting with Visual Studio 2013 Update 2"''</ref> An official extension allows Visual Studio 2012 to support TypeScript as well.<ref>[https://visualstudiogallery.msdn.microsoft.com/fa041d2d-5d77-494b-b0ba-8b4550792b4d TypeScript 1.0 Tools for Visual Studio 2012]</ref>

== History ==
Typescript was first made public in October 2012 (at version 0.8), after two years of internal development at Microsoft.<ref>{{cite web |url=https://www.infoworld.com/d/application-development/microsoft-augments-javascript-large-scale-development-203737 |title=Microsoft augments JavaScript for large-scale development |date=1 October 2012 |work=[[InfoWorld]] |publisher=[[International Data Group|IDG]] |accessdate=26 April 2015}}</ref><ref>{{cite web |url=https://blogs.msdn.com/b/typescript/archive/2014/04/02/announcing-typescript-1-0.aspx |title=Announcing TypeScript 1.0 |date=2 April 2014  |first=Jonathan |last=Turner |publisher=Microsoft |work=TypeScript Language team blog |accessdate=26 April 2015}}</ref> Early after the announcement, [[Miguel de Icaza]] praised the language itself, but criticized the lack of mature IDE support apart from [[Microsoft Visual Studio]], which is not available on Linux and OS X.<ref>{{cite web
| url=https://tirania.org/blog/archive/2012/Oct-01.html
| title=TypeScript: First Impressions
| date=2012-10-01
| author=[[Miguel de Icaza]]
| quote=''But TypeScript only delivers half of the value in using a strongly typed language to Unix developers: strong typing. Intellisense, code completion and refactoring are tools that are only available to Visual Studio Professional users on Windows. There is no Eclipse, MonoDevelop or Emacs support for any of the language features''
| accessdate=2012-10-12}}</ref><ref>{{cite web
| url=https://www.zdnet.com/microsoft-typescript-can-the-father-of-c-save-us-from-the-tyranny-of-javascript-7000005054/
| title=Microsoft TypeScript: Can the father of C# save us from the tyranny of JavaScript?
| date=2012-10-01
| publisher=[[ZDNet]]
| quote=''And I think this is a pretty big misstep. If you're building web apps that run on anything other than Windows, you're likely using a Mac and most likely not using Visual Studio. You need the Visual Studio plug-in to get the IntelliSense. All you get without Visual Studio is the strong-typing. You don't get the productivity benefits you get from IntelliSense.''.
| accessdate=2012-10-12}}</ref> {{As of|2013}} there is support in other IDEs, particularly in [[Eclipse (software)|Eclipse]], via a plug-in contributed by [[Palantir Technologies]].<ref>{{cite web |url=https://www.heise.de/developer/meldung/TypeScript-Unterstuetzung-fuer-Eclipse-1930408.html |title=TypeScript-Unterstützung für Eclipse |date=6 August 2013 |work=heise Developer |accessdate=26 April 2015}}</ref><ref>{{cite web |url=https://marketplace.eclipse.org/content/typescript#.VAmSNvm1bYg |title=TypeScript |work=Eclipse Marketplace |publisher=Eclipse Foundation |accessdate=26 April 2015}}</ref> Various text editors, including [[Emacs]], [[Vim (text editor)|Vim]], and [[Sublime Text|Sublime]] also support TypeScript.<ref>{{cite web |url=https://www.drdobbs.com/windows/working-with-typescript-in-visual-studio/240154792 |title=Working with TypeScript in Visual Studio 2012 |date=14 May 2013 |work=[[Dr. Dobb's Journal]] |first=Gastón |last=Hillar |accessdate=26 April 2015}}</ref>

TypeScript 0.9, released in 2013, added support for generics.<ref>{{cite web |url=https://www.theregister.co.uk/2013/06/18/typescript_update_0_9/ |title=TypeScript 0.9 arrives with new compiler, support for generics |date=18 June 2013 |work=[[The Register]] |accessdate=26 April 2015}}</ref> TypeScript 1.0 was released at [[Build (developer conference)|Build]] 2014.<ref>{{cite web|url=https://channel9.msdn.com/Events/Build/2014/3-576 |title=TypeScript |first=Anders |last=Hejlsberg |authorlink=Anders Hejlsberg |date=2 April 2014 |publisher=Microsoft |work=[[Channel 9 (Microsoft)|Channel 9]] |accessdate=26 April 2015}}</ref> [[Visual Studio 2013]] Update 2 provides built-in support for TypeScript.<ref>{{cite web |url=https://www.pcworld.com/article/2101920/microsoft-typescript-graduates-to-visual-studio.html |title=Microsoft TypeScript graduates to Visual Studio |first=Joab |last=Jackson |date=25 February 2014 |work=[[PC World]] |publisher=[[International Data Group|IDG]] |accessdate=26 April 2015}}</ref>

In July 2014, the development team announced a new TypeScript compiler, claiming 5× performance gains. Simultaneously, the source code, which was initially hosted on [[CodePlex]], was moved to [[GitHub]].<ref>{{cite web |url=https://blogs.msdn.com/b/typescript/archive/2014/07/21/new-compiler-and-moving-to-github.aspx |title=New Compiler and Moving to GitHub |date=21 July 2014 |publisher=Microsoft |work=TypeScript Language team blog |first=Jonathan |last=Turner|accessdate=26 April 2015}}</ref>

== Language design ==
TypeScript originated from the perceived shortcomings of JavaScript for the development of large-scale applications both at Microsoft and among their external customers.<ref>{{cite web|url=https://www.hanselminutes.com/340/what-is-typescript-and-why-with-anders-hejlsberg |title=What is TypeScript and why with Anders Hejlsberg |author=Anders Hejlsberg |publisher=www.hanselminutes.com |date=2012-10-05 |accessdate=2014-01-15}}</ref> Challenges with dealing with complex JavaScript code led to demand for custom tooling to ease developing of components in the language.<ref>{{cite web|url=https://blogs.msdn.com/b/somasegar/archive/2012/10/01/typescript-javascript-development-at-application-scale.aspx |title=TypeScript: JavaScript Development at Application Scale |author=S. Somasegar |publisher=msdn.com |date=2012-10-01 |accessdate=2013-11-27}}</ref>

TypeScript developers sought a solution that would not break compatibility with the standard and its cross-platform support. Knowing that the current ECMAScript standard proposal promised future support for [[class-based programming]], TypeScript was based on that proposal. That led to a JavaScript compiler with a set of syntactical language extensions, a superset based on the proposal, that transforms the extensions into regular JavaScript. In this sense TypeScript is a preview of what to expect of ECMAScript 6. A unique aspect not in the proposal, but added to TypeScript, is optional [[static typing]] that enables static language analysis, which facilitates tooling and IDE support.

=== ECMAScript 6 support ===
{{main|ECMAScript#ECMAScript Harmony (6th Edition)}}

TypeScript adds support for features such as classes, modules and an arrow function syntax as proposed in the upcoming ECMAScript 6 standard.

== Language features ==
TypeScript is a language extension that adds features to [[ECMAScript]] 5. Additional features include:
* [[Type signature|Type annotations]] and [[compile-time]] [[type checking]]
* [[Type inference]]
* [[Type erasure]]
* [[Interface (object-oriented programming)|Interfaces]]
* [[Enumerated type]]
* [[Mixin]]
* [[generic programming|Generic]]
* [[Namespace]]s
* [[Tuple]]
* [[Await]]

The following features are backported from ECMAScript 6: 
* [[Class (computer programming)|Classes]]
* [[Modular programming|Modules]]<ref>{{cite web|url=https://techcrunch.com/2012/10/01/microsoft-previews-new-javascript-like-programming-language-typescript/ |title=Microsoft Previews New JavaScript-Like Programming Language TypeScript |publisher=TechCrunch |date=2012-10-01 |author=Klint Finley | accessdate=2013-11-27}}</ref>
* Abbreviated "arrow" syntax for [[anonymous function]]s
* Optional parameters and default parameters

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.

=== Compatibility with JavaScript ===
TypeScript is a strict superset of JavaScript. As such, a JavaScript program is also a valid TypeScript program, and a TypeScript program can seamlessly consume JavaScript. TypeScript compiles to ES3-compatible JavaScript.<ref name="typescript-home-page">{{cite web |url=https://www.typescriptlang.org/ |title=Welcome to TypeScript |date= |work=typescriptlang.org |publisher=[[Microsoft]] |accessdate=26 April 2015}}</ref> By default the compiler targets ECMAScript 3, the current prevailing standard, and is also able to generate constructs used in ECMAScript 5.

With TypeScript, it is possible to use existing JavaScript code, incorporate popular JavaScript libraries, and call TypeScript-generated code from other JavaScript.<ref name="typescript-home-page" /> Type declarations for these libraries are provided with the source code.

=== Type annotations ===
TypeScript provides [[static typing]] through type annotations to enable [[type checking]] at [[compile time]]. This is optional and can be ignored to use the regular [[dynamic typing]] of JavaScript.
<source lang="typescript">
function add(left: number, right: number): number {
	return left + right;
}
</source>

The annotations for the primitive types are <code>number</code>, <code>boolean</code> and <code>string</code>. Weakly- or dynamically-typed structures are of type <code>any</code>.

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]] to infer types when types are not given. For example, the <code>add</code> method in the code above would be inferred as returning a <code>number</code> even if no return type annotation had been provided. This is based on the static types of <code>left</code> and <code>right</code> being <code>numbers</code>, and the compiler's knowledge that the result of adding two <code>numbers</code> is always a <code>number</code>. However, explicitly declaring the return type allows the compiler to verify correctness.

If no type can be inferred because of lack of declarations, then it defaults to the dynamic <code>any</code> type. A value of the <code>any</code> type supports the same operations as a value in JavaScript and minimal static type checking is performed for operations on <code>any</code> values.<ref>[https://www.typescriptlang.org/Content/TypeScript%20Language%20Specification.pdf TypeScript Language Specification p.24]</ref>

==== Declaration files ====
When a TypeScript script gets compiled there is an option to generate a ''declaration file'' (with the extension <code>.d.ts</code>) that functions as an [[interface (computing)|interface]] to the [[Component-oriented programming|component]]s 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 file]] found in [[C/C++]].
<source lang="typescript">
declare module arithmetics {
    add(left: number, right: number): number;
    subtract(left: number, right: number): number;
    multiply(left: number, right: number): number;
    divide(left: number, right: number): number;
}
</source>

Type declaration files can be written by hand for existing JavaScript libraries, as has been done for jQuery and Node.js.

A large collection of declaration files for popular JavaScript libraries is hosted on GitHub by [https://github.com/borisyankov/ borisyankov] in his [https://github.com/borisyankov/DefinitelyTyped DefinitelyTyped] repository. A command-line utility called <code>[https://github.com/DefinitelyTyped/tsd/ tsd]</code> is provided by the latter to help search and install declaration files from the repository.

=== Classes ===
TypeScript supports ECMAScript 6 classes that integrate the optional type annotations support.
<source lang="typescript">
class Person {
    private name: string;
    private age: number;
    private salary: number;

    constructor(name: string, age: number, salary: number) {
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    
    toString(): string {
        return `${this.name} (${this.age}) (${this.salary})`; // As of version 1.4
    }
}
</source>

=== Generics ===
TypeScript supports [[generic programming]].<ref>{{cite web|url=https://blogs.msdn.com/b/typescript/archive/2013/06/18/announcing-typescript-0-9.aspx |title=Announcing TypeScript 0.9 |work=TypeScript Language team blog |publisher=[[Microsoft]] |date=18 June 2013 |first=Jonathan |last=Turner}}</ref>

=== 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) utilizes [[immediately-invoked function expression]] of JavaScript to encapsulate code, whereas modules (formerly external modules) leverage JavaScript library patterns to do so ([[Asynchronous module definition|AMD]] or [[CommonJS]]).<ref>{{cite web|url=https://blog.oio.de/2014/01/31/an-introduction-to-typescript-module-system/ |title=An introduction to TypeScript’s module system |publisher=blog.oio.de |date=2014-01-31 |author=S&ouml;nke Sothmann | accessdate=2014-02-21}}</ref>

== Development tools ==

=== Compiler ===
The TypeScript compiler, named <code>tsc</code>, is [[Self-hosting|written in TypeScript]] that can be compiled into regular JavaScript that can be executed in any JavaScript engine in any host, such as 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.

There is also an [[Alpha test|alpha]] version of a client-side compiler in JavaScript, which executes TypeScript code on the fly, upon page load.<ref>{{cite web|url=https://github.com/niutech/typescript-compile|title=niutech/typescript-compile|date=|work=GitHub|accessdate=26 April 2015}}</ref>

The current version of the compiler supports [[ECMAScript|ECMAScript 3]] by default. An option is allowed to target ECMAScript 5 to make use of language features exclusive to that version. Classes, despite being part of the ECMAScript 6 standard, are available in both modes.

=== IDE and editor support ===
* [[Microsoft]] provides a [[Plug-in (computing)|plug-in]] for [[Visual Studio|Visual Studio 2012]] and [[Microsoft WebMatrix|WebMatrix]], full integrated support in [[Visual Studio|Visual Studio 2013]], [[Visual Studio|Visual Studio 2015]], and basic text editor support for [[Sublime Text]], [[Emacs]] and [[Vim (text editor)|Vim]].<ref name="blogs.msdn.com">{{cite web| author= Olivier Bloch|title = Sublime Text, Vi, Emacs: TypeScript enabled!|url = https://blogs.msdn.com/b/interoperability/archive/2012/10/01/sublime-text-vi-emacs-typescript-enabled.aspx|publisher = [[Microsoft]]|date = 2012-10-01|accessdate = 2012-10-28 }}</ref>
* [[Visual Studio Code]] is an open-source, cross-platform source code editor developed by Microsoft based on Electron. It supports TypeScript in addition to several other languages, and offers features like debugging and intelligent code completion.
* [[JetBrains]] supports TypeScript with code completion, refactoring and debugging in its IDEs built on IntelliJ platform, such as [[PhpStorm]] 6, [[WebStorm]] 6, and [[IntelliJ IDEA]],<ref>{{cite web|title=TypeScript support in WebStorm 6|url=https://blog.jetbrains.com/webide/2013/02/typescript-support-in-webstorm-6|publisher=JetBrains}}</ref> as well as their Visual Studio Add-in and extension, [https://www.jetbrains.com/resharper ReSharper] 8.1.<ref>{{cite web|title=TypeScript support in ReSharper 8.1|url=https://blog.jetbrains.com/dotnet/2013/10/28/typescript-support-resharper-81/|publisher=JetBrains}}</ref>
* Atom editor has a [https://atom.io/packages/atom-typescript TypeScript Plugin] by [[Basarat Ali Syed|Basarat]] with support for code completion, navigation, formatting, and fast compilation.
* The online [[Cloud9 IDE]] and [[Codenvy]] support TypeScript.
* [https://github.com/Everlaw/nbts A plugin] is available for the [[NetBeans|NetBeans IDE]].
* [https://github.com/palantir/eclipse-typescript A plugin] is available for the [[Eclipse (software)|Eclipse IDE]] (version Kepler)
* [https://typecsdev.com TypEcs] is available for the [[Eclipse (software)|Eclipse IDE]].
* [https://github.com/Railk/T3S T3S] and [https://sublime.wbond.net/packages/Better%20TypeScript Better TypeScript] are available for [[Sublime Text]].
* The Cross Platform Cloud IDE [[Codeanywhere]] supports TypeScript.

=== Integration with build automation tools ===
Using [[Plug-in (computing)|plug-ins]], TypeScript can be integrated with [[build automation]] tools, including Grunt (grunt-ts<ref>{{cite web|url=https://github.com/basarat/grunt-ts|title=TypeStrong/grunt-ts|date=|work=GitHub|accessdate=26 April 2015}}</ref>), [[Apache Maven]] (TypeScript Maven Plugin<ref>{{cite web|url=https://github.com/ppedregal/typescript-maven-plugin|title=ppedregal/typescript-maven-plugin|date=|work=GitHub|accessdate=26 April 2015}}</ref>) and [[Gradle]] (TypeScript Gradle Plugin<ref>{{cite web|url=https://github.com/sothmann/typescript-gradle-plugin|title=sothmann/typescript-gradle-plugin|date=|work=GitHub|accessdate=26 April 2015}}</ref>).

== See also ==
{{Portal|Free software}}
* [[Closure Compiler]]
* [[JavaScript]]
* [[ECMAScript]]
* [[Dart_(programming_language)|Dart]]

== References ==
{{reflist|30em}}

== External links ==
* {{official website|https://www.typescriptlang.org/}}
* [https://github.com/Microsoft/TypeScript TypeScript] project at [[GitHub]]
* [https://go.microsoft.com/fwlink/?LinkId=267121 TypeScript Language Specification]
* [https://github.com/jbaron/cats CATS Cross Platform TypeScript Editor]
* [https://channel9.msdn.com/Events/Build/2013/3-314 Build 2013 presentation]
* [https://github.com/dzharii/awesome-typescript Awesome-Typescript: A community-supported list of tools and resources related to TypeScript]

{{JavaScript|state=collapsed}}
{{Microsoft APIs}}
{{NodeJs}}

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