How to distinguish a method property from a bound callback property?

[dko-slapdash]

Suggestion

I expected ThisParameterType helper to be able to distinguish between methods (unbound function properties) and callbacks (bound functions), but it doesn't want to do it:

class Cls {
  method() {}
  callback = () => {}
}

type aaa = ThisParameterType<Cls["callback"]>;
// Aaa = unknown

type Bbb = ThisParameterType<Cls["method"]>;
// Bbb = unknown -- WHY? How to distinguish?

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🔍 Search Terms

method property from a bound callback property this

💻 Use Cases

I want to enumerate all plain properties of some type (e.g. a class instance), but skip methods. Currently I do it with:

export type NonMethodPropertyNames<T> = {
  [K in keyof T]: T[K] extends Function ? never : K;
}[keyof T];

export type NonMethodProperties<T> = Pick<T, NonMethodPropertyNames<T>>;

but unfortunately, this NonMethodProperties also skips callback properties. E.g. in this example:

class Cls {
  constructor(public a = 10, public callback: () => void) {}
  method() {}
}

...I would expect NonMethodProperties<Cls> to return { a: number; callback: () => void }, but unfortunately it skips not only method, but also callback since I couldn't find a way to distinguish them.

[MartinJohns]

The method in your class don't have a this argument, so ThisParameterType<> does not work on them. There's the open issue #28548 to automatically add a this argument to class methods.

[typescript-bot]

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