Add batchedEffect()

[justinfagnani]

This adds a batchedEffect(cb) utility that synchronously runs its callback when dependencies are updated inside a batch() call.

const a = new Signal.State(0);
const b = new Signal.State(0);

batchedEffect(() => {
  console.log("a + b =", a.get() + b.get());
});

// Logs: a + b = 0

batch(() => {
  a.set(1);
  b.set(1);
});

// Logs: a + b = 2

[NullVoxPopuli]

why const arrow instead of function batch() {}?
(is this personal preference, or some perf/debugging thing I don't know about? 😅 )

[justinfagnani]

Personal preference - I just use arrow functions for everything possible.

I supposed there's a slight theoretical perf benefit from not having a mutable binding, if the VM correctly elides the TDZ check for this case. Maybe some bundlers take advantage of this too? There's also of course a theoretical perf hit from un-elided TDZ checks.

I just personally think that arrow functions are the correct function semantics, and use the function to highlight cases where this might be non-lexical.

[justinfagnani]

Oops, we should return an unsubscribe function here.

[justinfagnani]

@NullVoxPopuli fyi

[NullVoxPopuli]

womp, want to throw up another PR? <3

[lennartbuit]

typo: notify