The definitions contain externs for use with the Closure compiler (aka JSCompiler). Passing these files to the –externs parameter of a compiler pass allows using type annotations for AngularJS objects. For example, AngularJS’s $scope objects can be annotated as:
This allows JSCompiler to type check accesses to scope, give warnings about missing methods or incorrect arguments, and also prevents renaming of property accesses with advanced compilation.
The externs are incomplete and maintained on an as-needed basis, but strive to be correct. Externs for individual modules should be added in separate files.