How to implement computed fields

[maku]

I would like to have computed fields for my form. E.g. I implement an invoice form with an items array (quantity, price for one). Then I have to compute certain fields on the items array and summing for the whole invoice, tax etc.

The computed fields should also be input fields (but disabled)

An approach I could imagine would be to subscribe to the data store and update certain fields...

But is this a "good" way. Is there a "felte" way to do this?

TIA

[pablo-abc]

There's no "official" or "Felte" way to do this. Computed values are something frameworks are generally good at. If you're using Svelte, for example:

<script>
  const { form, data } = createForm({ /* ... */ });

  $: computed = $data.value /* Do something here with $data.value */;
</script>
<form use:form>
  <!-- .... -->
  <input disabled value={computed}>
</form>

Svelte is specially good at this since the $: syntax works perfectly for this.

If you're using Solid/React/Preact then the "signal" call can be used to compute a value. E.g. for Solid:

function Form() {
  const { data, form} = createForm({ /* ... */ });
  const computed = () => data(($data) => $data.value /* Do something with the value */)

 return (
    <form use:form>
      {/* ... */}
      <input disabled value={computed()} />
    </form>
  )
}