What is the best way to design a versatile instanceof function that returns the object if it matches the specified type?

I am currently working on developing a function with this structure:

function isInstance<T>(s: T): T | boolean {
  return (s instanceof T) && s;
}

The purpose of this function is to return the value as that type if it is an instance, otherwise it returns false.

When I attempt to compile this code, I encounter the following error message:

'T' only refers to a type, but is being used as a value here.

My understanding is that I need to pass a T there in order to determine if it is of that type. However, TypeScript types do not exist at runtime which could be causing the issue. I am unsure of an alternative solution that would work in this case.

typescripttypesinstanceof

Answer №1

While browsing the web, I came across this interesting code snippet. It appears to have some functionality, but I'm not entirely sure how it operates.

type NewType<S> = new (...args: any[]) => S;

function checkInstance<S>(obj: any, type: NewType<S>) {
  return obj instanceof type && obj;
}

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