TypeScript class prototype includes instance member

[luokuning]

TypeScript Version: TypeScript official playground

Search Terms:

Code

class Hello {
    abc = {
        a: 'l',
        b: 1,
    }
    k = (prop: keyof typeof Hello.prototype.abc) => {
        console.log(prop)
    }
}

Expected behavior:

TypeScript compiler should complain about the Hello.prototype.abc, because abc is an instance property not in the Hello.prototype.

Actual behavior:

The code works fine in TypeScript playground, no compiling errors.

Playground Link: http://www.typescriptlang.org/play/index.html#src=class%20Hello%20%7B%0D%0A%20%20%20%20abc%20%3D%20%7B%0D%0A%20%20%20%20%20%20%20%20a%3A%20'l'%2C%0D%0A%20%20%20%20%20%20%20%20b%3A%201%2C%0D%0A%20%20%20%20%7D%0D%0A%20%20%20%20k%20%3D%20(prop%3A%20keyof%20typeof%20Hello.prototype.abc)%20%3D%3E%20%7B%0D%0A%20%20%20%20%20%20%20%20console.log(prop)%0D%0A%20%20%20%20%7D%0D%0A%7D

[RyanCavanaugh]

Duplicate #11558

[RyanCavanaugh]

Also #20922

[jcalz]

(I'm commenting here because the linked issues are locked)

One could imagine that instance-only properties could be made optional in the prototype type. But I'm sure this would break all kinds of things (I'm pretty sure x instanceof C narrows x to C['prototype'], which would be a funny thing to do if the prototype were wider than C) and not add much value.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.