SolidJS•2y ago

How can I skip the first effect run with createEffect?

I have a createEffect hook that runs when my signal does. Awesome. What I don't want, is for the effect to run when the initial signal value is set. I tried the following without success:

const [getVal, setVal] = createSignal("initial");

let firstEffectHasRun = false;
createEffect(() => {
  if (firstEffectHasRun) {
    console.log("Boom!");
  } else {
    firstEffectHasRun = true;
  }
});

const [getVal, setVal] = createSignal("initial");

let firstEffectHasRun = false;
createEffect(() => {
  if (firstEffectHasRun) {
    console.log("Boom!");
  } else {
    firstEffectHasRun = true;
  }
});

I don't get why this doesn't work since firstEffectHasRun should be cached since it's used within the callback.

2 Replies

thetarnav•2y ago

that effect is not subscribing to anything, so why would it rerun? you can do this:

let init = true;
createEffect(() => {
  // track
  const val = value()
  // skip initial
  if (init) return init = false
  // boom
  console.log("Boom!")
});

let init = true;
createEffect(() => {
  // track
  const val = value()
  // skip initial
  if (init) return init = false
  // boom
  console.log("Boom!")
});

or use on:

createEffect(on(
  // track
  value,
  // boom
  () => console.log("Boom!"),
  // skip initial
  { defer: true }
))

createEffect(on(
  // track
  value,
  // boom
  () => console.log("Boom!"),
  // skip initial
  { defer: true }
))

RATIU5OP•2y ago

Completely missed that part when copying over. And your first method worked fine, I was not aware about the on function. My guess is that since I had my subscription within the conditional statement it did not run. It works now, thank you!

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How can I skip the first effect run with createEffect?