[joewood1972]

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.

[seanmcdirmid]

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.