`z.instanceof` does not accept abstract classes

[WillsterJohnson]

In #1065, z.instanceof rejects classes with a private constructor. This can be resolved by using z.custom, but this syntax isn't ideal and repeats itself between the type param and the right hand side of instanceof operator.

A similar issue appears when using an abstract class, is there anything that could be done about that?

abstract class foo {
  constructor() {}
}

z.instanceof(foo);
// Argument of type 'typeof foo' is not assignable to parameter of type 'new (...args: any[]) => any'.
//  Cannot assign an abstract constructor type to a non-abstract constructor type. ts(2345)

This can be worked around using the above, but typescript does allow for parameter type abstract new (...args: any[]) => any, which could be used either in place of or in union to the existing parameter type on z.instanceof

Failing that, a class is just a different syntax for defining a function, and classes can be passed to parameter type Function. This allows for incorrect usage by passing a normal, non-class function, but I expect most users of Zod to understand the difference on the basis of a) they're competent enough to be using TypeScript and b) they're using Zod, a schema-base parser/validator.

// this has no issues with very strict TS compiler options
function parse(x: Function, y: unknown) {
  return y instanceof x;
}

// this solves the abstract issue, and prevents passing incorrect subtypes of `Function`

/** this union is not necessary and will work with only the abstract variant. The union is to be more verbose */
type MaybeAbstractClass = (abstract new (...args: any[]) => any) | (new (...args: any[]) => any);

function parse(x: MaybeAbstractClass, y: unknown) {
  return y instanceof x;
}

[colinhacks]

I found a fix for this but it requires bumping the minimum version to TS4.4 which I'd rather avoid until I release another major version.

[stale[bot]]

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