Default param causes ts-check to fail

ts-check-bug-simpler.js

const Obj = {
    x: 1,
    f: (y = Obj.x) => {}
};

Obj.x; // No definition found for 'x'

Exactly.
And amusingly, just accidentally caught this approach in that very editor:
https://www.typescriptlang.org/play/main-3.js

// whoa, no typescript and no compilation!

😄

(Sorry for spam, just had to share. Happy holidays :] )

OH, and BTW, if you are using modern-ish JS, you'll probably need do add few libs to "have" some features missing in current TS standard defs; for example in service worker I needed

/// <reference lib="webworker" />
// `Property 'finally' does not exist on type 'Promise<void>'`, introduced with es2018
/// <reference lib="es2018.promise" />

Hah, nice! Happy holidays!