> But what if you got it from an outside function, such as init(), and it was an object instead? Then you would have to guarantee that the return value of init() would not change between statements.

Then even in a synchronous context you'd have no guarantee that it wouldn't be modified:

  function soSomethingSync() {
    window.someObj.someProp = 12;
  }

  let x = window.someObj;

  soSomethingSync();

  console.log(x)

This has nothing whatsoever to do with sync vs async.

It is one of the main reasons people like immutability/functional programming. But that's its own topic.

Then this is not related to async/await but regardless even then JavaScript has always had the ability to change the writability of properties such that trying to change a property in an object will yield a no-op with Object.defineProperty, and now with newer features like Object.freeze and private properties.