Incorrect refinement using instanceof

[vkurchatkin]

Example:

class A {
  foo(x: string) {
  }
}

class B extends A {
  foo(x: number) {
    return x.toFixed();
  }
}

function test(a: A | B | {}) {
  if (a instanceof A) {
    a.foo('')
  }
}

a is refined to be an A instead of A | B, which leads to a runtime error.

[thecotne]

you should not be able to extend class and change signature/type of existing functions

both typescript and flow do this

try typescript
try flow

[vkurchatkin]

That is a separate issue. Refinement is still incorrect

[JSMonk]

Fixed in 0.0.44