Error inheritance bug

[elderapo]

TypeScript Version: 3.0.0-dev.201xxxxx

Search Terms: error inheritance

Code

class CustomError extends Error {}

try {
  throw new CustomError();
} catch (ex) {
  console.log(ex instanceof CustomError);
}

Expected behavior: should print true in both TypeScript and vanilla JS.

Actual behavior: if compiled with TypeScript and then ran in browser/node environment prints false but if ran without compilation prints true.

Playground Link: http://www.typescriptlang.org/play/#src=class%20CustomError%20extends%20Error%20%7B%7D%0D%0A%0D%0Atry%20%7B%0D%0A%20%20throw%20new%20CustomError()%3B%0D%0A%7D%20catch%20(ex)%20%7B%0D%0A%20%20console.log(ex%20instanceof%20CustomError)%3B%0D%0A%7D%0D%0A

Related Issues:

[DanielRosenwasser]

https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#extending-built-ins-like-error-array-and-map-may-no-longer-work

Duplicate of #12123

[RyanCavanaugh]

https://github.com/Microsoft/TypeScript/wiki/FAQ#why-doesnt-extending-built-ins-like-error-array-and-map-work