window and window.location aren't part of javascript. They are part of the javascript api that standard browsers provide.
It's fair to point out that browser api is confusing. You might not think of setting a property as kicking off an asynchronous operation, especially if it seems to has instantaneous effect at first.
But the basic control flow logic of that code is wrong. Confusion about whether a side-effect from an api call might bail you out from your error is beside the point.
web_sys lets you call window.location, which returns a Location, which has href and set_href methods. They do the same thing the native APIs do, as that is their purpose.
