TypeScript adds support for features such as classes, modules, and an arrow function syntax as defined in the ECMAScript 2015 standard.

TypeScript is a language extension that adds features to ECMAScript 6. Additional features include:

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.

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 in .

TypeScript supports ECMAScript 2015 classes that integrate the optional type annotations support.

The current version of the compiler supports ECMAScript 5 by default. An option is allowed to target ECMAScript 2015 to make use of language features exclusive to that version (e.g. generators). Classes, despite being part of the ECMAScript 2015 standard, are available in both modes.