Microsoft’s Anders Hejlsberg has introduced TypeScript, a programming language which is a superset of JavaScript and which compiles to JavaScript code.

The thinking behind TypeScript is that JavaScript is unsuitable for large projects.

“JavaScript was never designed to be a programming language for big applications,” says Microsoft’s Anders Hejlsberg, inventor of C#. “It’s a scripting language.”

The ubiquity of JavaScript makes it remarkably useful though, with that now extending to the server thanks to projects like node.js. Microsoft is using node.js for its Azure Mobile Services.

TypeScript therefore lets you use features including type annotations, classes, modules and interfaces to make large projects more robust and maintainable.

Variable names are preserved when TypeScript is compiled. Further, since TypeScript is a superset, any JavaScript code can be pasted into a TypeScript project. The compiler is open source and you can download an early version here.

Microsoft is also trying to stay close to the specification for Ecmascript 6, the proposed next iteration of the official JavaScript standard, where relevant.

There is tooling for Visual Studio including a language service to provide code hinting, syntax highlighting and the like.

TypeScript differs from projects like Google Web Toolkit or Script#, both of which also emit JavaScript, in that it does not compile from one language into another; rather, it compiles into a reduced version of itself.

Why is Microsoft doing this? That is the interesting question. I would conjecture that it is partly self-interest. Microsoft itself has to write increasing amounts of JavaScript, for things like Office Web Apps (apparently written in Script#) and the new Azure portals. Azure Mobile Services uses JavaScript as mentioned above. JavaScript is also one of the options for coding apps for Windows 8. Better tools will help Microsoft itself to be more productive.

That said, the arrival of TypeScript will re-ignite the debate about whether Microsoft, while not anywhere close to abandoning .NET, is nevertheless drifting away from it, towards both native code in Windows and now JavaScript in the managed code space.

More information from Microsoft’s S Somasegar here.