[zodester]

React Native follows this pattern by moving most JS processing off the main thread allowing scrolling and other input to happen without blocking for a response from the JS VM. However this does end up causing a lot of problems with text input and gestures as now you have a sync issue between the threads, if you get caught processing a bunch of stuff in the JS thread the app may appear to be responsive with scrolling but nothing happens in response to button taps or text insertion. It is the only way RN was going to work on lower end hardware though so probably is the right solution if you assume running react everywhere is a good idea.

[mike_hearn]

Yes, making GUIs responsive isn't as simple as just "don't run stuff on the UI thread". There are good reasons to run stuff there even if you're going to hang up the app for a brief period, namely, the user won't see partial/incorrect updates like non-syntax highlighted text or incorrectly clipped shapes, and - especially important - it means you can't end up with invalid GUI states like the user pressing a button that does X and then immediately pressing another button that does the opposite of X, where you should have disabled the other button but didn't get to it in time. Web apps have this sort of problem if they aren't using enough JS, and it can cause all kinds of weird bugs and errors.

The reality is that moving things off the UI thread is always a calculated engineering decision. It can be worth it, but it complicates the code and should only be done if there's a realistic chance of the user noticing.