Assuming assert existed, it would almost certainly be judging its value for being falsy, while the ?? operator judges its LHS for being nullish, which is a narrower category. For strings, this affects whether the empty string is acceptable or not.
Fair, this is a good example of when != is actually the right choice (instead of !==). However, on web browsers, this will log an assertion failure to the console, but it will not throw an exception. It's also not suitable for the original context, where the non-null value was extracted into a variable.
