Monkeypatch Math.random(), new Date() and Date.now() during render() in dev

Was talking with Adam Wolff today about rxjs and there are a ton of common bugs with these functions. You’re gonna have a bad time if you use these in React render() methods too – if we monkeypatched these to warn in __DEV__ we could prevent some bugs. @jordwalke seemed to like the idea too.

[syranide]

@steveluscher That sounds kind of fragile to me, I think time is ubiquitous enough that Date.now() should be exported by React as React.now(). So that when any rendering inside React takes place, time is frozen and all subsequent calls to React.now() returns that same time.

For React.renderComponentToString the frozen time would also be added to the root element next to the checksum, which would be used for the initial rendering on the client when reusing the DOM.

Aside from just fixing mismatches between client and server rendering, it would also prevent edge-case inconsistencies in rendering. Two identical timer components can currently show slightly varying times, or say an item could show as expired in one place and not expired in another if the timing is just right. This would prevent that entirely.

@petehunt Any spontaneous reaction?

[gaearon]

This has been inactive for over a year, and it doesn’t appear like there any plans to do this. With the explosion of JavaScript build tools and polyfills, we have been trying to be careful to not add surprises or touch the built-ins, and I think it has been the right call. React Native is actually running into some issues right now because of conflicting polyfills, and it’s great we’ve been able to avoid those so far by not touching the built-ins.

I’m closing this but please let me know if I’m making a mistake and we should reopen. Thanks!