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# and creator of Delphi and Turbo Pascal, has worked on the development of TypeScript.TypeScript is designed for development of large applications and transcompiles to JavaScript. As TypeScript is a superset of JavaScript, any existing JavaScript programs are also valid TypeScript programs.TypeScript supports header files which can contain type information of existing JavaScript libraries, enabling other programs to use objects defined in the header files as if they were strongly typed TypeScript objects. There are third-party header files for popular libraries like jQuery, MongoDB, Node.js, and D3.js.TypeScript is licensed under the Apache 2 License.