Infer arguments for abstract class in typescript

Question

I'm trying to get the arguments for typescript classes and functions.

export type CtorArgs<TBase> = TBase extends new (...args: infer TArgs) => infer Impl ? TArgs : never;
export type AbsCtorArgs<TBase> = TBase extends {constructor: (...args: infer TArgs) => infer Impl} ? TArgs : never;
export type FuncArgs<TBase> = TBase extends (...args: infer TArgs) => infer Impl ? TArgs : never;

function RegularFunction(a:string,b:number){}
class RegularClass{
    constructor(a:string,b:number){}
}    
abstract class AbstractClass{
    constructor(a:string,b:number){}
}


type thing = [
    CtorArgs<typeof RegularClass>,
    FuncArgs<typeof RegularFunction>,
    AbsCtorArgs<typeof AbstractClass>,
    CtorArgs<typeof AbstractClass>,
    FuncArgs<typeof AbstractClass>
];

But for some reason abstract classes don't return arguments of their constructors. I suspect this is because the new keyword isn't available on abstract classes . Does anybody know how to get those arguments which do actually exist for an abstract class constructor?

And no, this isn't about instantiating a abstract classes, this is about dependency injection to a class that inherits from an abstract class and the arguments to that class. See here

Answer 1

It is possible to infer parameters of abstract class. You just need to add abstract keyword before new .

See example:

abstract class AbstractClass {
    constructor(a: string, b: number) { }
}
export type InferAbstract<T> = T extends abstract new (...args: infer Args) => infer _ ? Args : never;

type Result = InferAbstract<typeof AbstractClass> // [a: string, b: number]

But you don't even need to use some custom utility types. You can use built it [ConstructorParameters][1] which was introduced in TS 3.1