Signals & Deferrable — Series 2

Preview — 3 of 10 questions

Why does the second signal notify less often?

javascript

a = signal<string[]>([]);
b = signal<string[]>([], { equal: (x, y) => x.length === y.length });

Ab only accepts arrays of the same length; other writes throw

Bequal is only used by computed(), never by a writable signal

Cequal makes the signal deeply compare its contents

Dequal decides whether a write counts as a change. By default signals compare with Object.is, so any new array notifies; b treats same-length arrays as equal and skips the notification

What does wrapping the read change?

javascript

effect(() => {
  const id = this.selectedId();
  const all = untracked(() => this.allItems());
  this.log(id, all.length);
});

AIt reads a stale value from the previous tick

BIt defers the read until after the effect returns

CIt reads the current value without registering a dependency — the effect re-runs when selectedId changes, but not when allItems does

DIt prevents other effects from reading allItems concurrently

What is onCleanup for?

javascript

effect((onCleanup) => {
  const id = setInterval(() => this.poll(this.url()), 1000);
  onCleanup(() => clearInterval(id));
});

AIt runs only once, when the component is destroyed

BIt runs before each re-run of the effect and once on destroy — so the previous interval is cleared before a new one starts when url changes

CIt runs after the effect body, in the same tick, always

DIt cancels the effect permanently

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