Although static typing is amazing, most of the frontend libraries we use are built with JavaScript, which is dynamically typed. Since we'd want to use TypeScript in Angular, not having type definitions in the code that uses external JavaScript libraries is a big issue; it prevents us from taking advantage of the compile-time type checking.
TypeScript was built keeping these points in mind. In order to allow the TypeScript compiler to take care of what it does best, we can use the so-called ambient type definitions. They allow us to provide external type definitions of the existing JavaScript libraries. This way, they provide hints to the compiler.
Fortunately, we don't have to create ambient type definitions for all JavaScript libraries and frameworks we use. The community and/or the authors of these libraries have already published such definitions online; the biggest repository resides at https://github.com/DefinitelyTyped...
