I agree that in most cases the if (!(x instanceof Y)) {...} is the best approach, but in some cases creating an isY(x) function so you can if (!isY(x)) {...} is worthwhile.
I’m a typescript novice, and I’ve bumped into this S/O question a bunch of times over the last few weeks, so for the googlers the typescript way to do this is to create a typeguard like this:
typeGuards.ts
export function isHTMLInputElement (value: any): value is HTMLInputElement {
return value instanceof HTMLInputElement
}
usage
if (!isHTMLInputElement(x)) throw new RangeError()
// do something with an HTMLInputElement
I guess the only reason why this might be appropriate in typescript and not regular js is that typeguards are a common convention, so if you’re writing them for other interfaces, it’s reasonable / understandable / natural to write them for classes too.
There’s more detail about user defined type guards like this in the docs
