Hacker News Reader

Comment by moomin | Hacker News Reader

Yes, but immutability means that reference checks are enough to spot unchanged areas. And we're not in HPC land right now, we're writing JavaScript. In that world, Om (immutable) is vastly faster than Backbone, Knockout, Angular, Ember &c (mutable). Partially because, when you can reason more clearly, it's easier to do something about the performance.

View on HN

Reference checks are conservative in spotting unchanged areas (if true, definitely no change, if false, maybe no change) unless all values are internalized (a bit expensive to do that). Also, diffing is only needed at all when you need to compare values anyways; dirty bits are otherwise sufficient to mark changes.

I'm not really familiar with the web ecosystem, but why would it differ so much from say C#/WPF? or a system based on change propagation instead of diffing?

If everything is immutable then a reference check is all you need. They key is to avoid deep copies. Observables are problematic when changes can ripple through your model/view-model - resulting in multiple DOM changes. This equally applies to WPF.

WPF has a retained scene graph, so no diffs are necessary, all changes are just O(1).

Reference equalities only work to know what really hasn't changed, they of course can't tell you that two values are still equal even if their references are different (unless compketely internalized, of course). For react, that's fine: it's just some extra work if false inequality is encountered, there are other applications where its not ok.

Reply on news.ycombinator.com