SolidJS•13mo ago

How to properly memoize children?

I have a small reactivity puzzle that I'm a little stumped on. I'm not sure if I just haven't structured my signals granularly enough, or simply don't understand something, or both. Essentially I have a pattern like this, in order to implement a list of dynamic inputs (1-N of them):

<For each={inputStates()>
  {(inputState) => (
    <ValidTag valid={inputState.valid}>
      <Input
        placeholder={inputState.value}
        onInput={[
          (input_id: string, event) => {
            updateInput(event.currentTarget.value)
          },
          inputState.input_id,
        ]}
      />
    </ValidTag>
  )}
</For>

<For each={inputStates()>
  {(inputState) => (
    <ValidTag valid={inputState.valid}>
      <Input
        placeholder={inputState.value}
        onInput={[
          (input_id: string, event) => {
            updateInput(event.currentTarget.value)
          },
          inputState.input_id,
        ]}
      />
    </ValidTag>
  )}
</For>

Where the .valid property is being computed and set externally, as a part of updateInput. There's where the problem comes in - I do want the children of <For> to update with the signal, and for <ValidTag> to update, but I do not want the <Input> to update - it has no need to after initialization, and it re-rendering causes focus to blur (but also is just undesirable). So, the title suggests one path I could guess out of this (memoizing <Input> manually), though a naive attempt did not work. I could guess that splitting the .valid signal and passing a list of signals, or a store, into <For> might also work. But mainly, I just want to know what the idiomatic way to do this is - or any way, really. I'm pretty stumped.

2 Replies

jon vuriOP•13mo ago

One other difficulty I mentioned here that might already be obvious from my example, but I'm not exactly sure how to do said splitting of the signals - I've already experimented with that some, and the wall I'm hitting is how to cross the <For> boundary - that itself needs to be a signal in order to update the list, otherwise nothing updates. But it seems that as long as it is a signal, everything updates (which does make sense). I initially tried using a store, thinking that because it would be different signals for each property, it would work as expected, but then I ran into that 'boundary' (because the store object itself was not changing reference)

thetarnav•13mo ago

How does the data structure look like and how do you update it When using a For the data structure can’t be immutable and stored in a single signal. You have to introduce more points of change, here, for the . valid property, and mutate it, instead of the whole inputState object

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How to properly memoize children?