That's tricky too. You can't just remove window.prompt, or users won't be able to use pages that rely on it for critical input. So what do you do? window.prompt is a synchronous API; you have to return something to the code that called it. You might say "well, just suspend that function and let the user interact with the rest of the page". But by doing that you've introduced coroutines to JavaScript (since "interacting with the rest of the page" means "running JS"), which is a huge change that comes with a mountain of tricky interactions. Even if it could be made to work (which most browser vendors think is impossible), it would still break pages that didn't expect random state to change across the window.prompt call.