Accessing property on super should be a type error

[trusktr]

TypeScript Version: 3.7.2

Search Terms:

typescript property access super undefined

Code

    class Base {
        n = 3
    }

    class Foo extends Base {
        test() {
            console.log(super.n) // type system says it should be a number, but it is undefined
        }
    }

    new Foo().test() // logs "undefined"

Expected behavior:

Should be some sort of type error, because clearly it is undefined

Actual behavior:

no error until runtime

Playground Link

[fatcerberus]

This might be a design limitation - TypeScript can’t currently distinguish between prototype properties and own properties of a class type. The type of super is Base, and Base-the-type has a property n, so the typechecker is satisfied.

[Jack-Works]

#54056