TypeScript interface for function with properties

Question

I'm using TypeScript on an Angular.js project and testing with Jasmine.

When I mock a method on an object using spyOn, Jasmine replaces the method with a function that has a calls property so you can do, for instance, thing.method.calls.count().

The problem is that the TypeScript compiler doesn't know about the calls property on the method and gives a compiler error:

property 'calls' does not exist on type '() => IPromise<IReport[]>'

How do I fix this error? Do I need to define a new interface that has a function signature as well as an object property? I've tried monkeying around with different interface configurations, but without luck so far.

Answer 1

How do I fix this error?

Basically add to the Function interface in a file like globals.d.ts. Demo:

interface Function {
    calls: any;
}

var foo = ()=>null;
foo.calls; // okay 

This trick is covered here : https://basarat.gitbooks.io/typescript/content/docs/types/lib.d.ts.html