At first - it is very similar to C#, that makes .NET developer's life easy.
At second - TypeScript is a superset of JavaScript, and you can mix "pure" JavaScript code with "typed" TypeScript. It is very important in case you have a lot of JavaScript in your project and want to take advantage of modern web technologies. I have an example - my IZWebFileManager project
At third (but not less important) - it has Lambda expression
I am using JQuery AJAX, and used to write such code:
This pattern became routine and very annoying.
But TypeScript bring the solution:
It is much simple, no need to care of what 'this' is anymore. It just does all this annoying routine behind the scene. There is compiled JavaScript output:
It worth to move to TypeScript just because it is a great feature