Extract function parameters or change function return type in mapped types

Search Terms

extract function parameters
change function return type

Suggestion

Allow mapped types to change the return type of a function

Use Cases

I am writing a mocking framework. My system under test might be like this:

MyClass{
    myClassFunction(paramOne: string, paramTwo: number): string{}
}

but in my mocking framework I want to do this:

mockedObject
    .withFunction("myClassFunction")
    .withParameters("paramOneValue", 123)
   .wasCalled();

to do the withParameters I need to type a function with the same parameters as defined on my class but with a different return type.

Checklist

My suggestion meets these guidelines:
[ ] This wouldn't be a breaking change in existing TypeScript / JavaScript code
[ ] This wouldn't change the runtime behavior of existing JavaScript code
[ ] This could be implemented without emitting different JS based on the types of the expressions
[ ] This isn't a runtime feature (e.g. new expression-level syntax)

Comienza examinando las capacidades de TypeScript para mapped types y function types en relación con el ejemplo de mocking-framework. Determina cómo deberían expresarse la extracción de parámetros y el reemplazo del tipo de retorno, preservando al mismo tiempo el comportamiento existente de TypeScript y JavaScript. Se considera completado cuando se admite la transformación de tipos solicitada y los parámetros de la función mockeada del ejemplo se comprueban correctamente.