@mayfail/svelte

Svelte integration for mayfail.

useMayfail runs a synchronous or asynchronous operation and exposes its latest result as Svelte stores, without requiring try/catch in event handlers.

It is safe to use with overlapping async calls: every execute resolves with its own result, while only the latest call can update the stores.

Installation

pnpm add @mayfail/svelte

Svelte 4 or later is required.

Usage

Pass an operation to useMayfail, then call execute from an event handler.

<script lang="ts">
  import { useMayfail } from "@mayfail/svelte";

  let name = "Ada";
  const { execute, error, isPending, value } = useMayfail(async (nextName: string) => {
    const response = await fetch("/api/profile", {
      method: "POST",
      body: JSON.stringify({ name: nextName }),
    });

    if (!response.ok) throw new Error("Unable to save profile");

    return response.json() as Promise<{ id: string; name: string }>;
  });
</script>

<form on:submit|preventDefault={() => void execute(name)}>
  <label>
    Name
    <input bind:value={name} />
  </label>
  <button disabled={$isPending} type="submit">
    {$isPending ? "Saving…" : "Save profile"}
  </button>
  {#if $error}<p role="alert">{$error.message}</p>{/if}
  {#if $value}<p>Saved {$value.name}</p>{/if}
</form>

API

useMayfail(operation) returns:

• execute(...arguments): runs operation and always resolves to [value, null] or [null, error].
• value: a readable store containing the latest successful value, or null.
• error: a readable store containing the latest error, or null.
• result: a readable store containing the latest result tuple, or null before the first execution or after reset.
• isPending: a readable boolean store for the latest execution.
• reset(): clears the stored result and pending state. Any execution already in flight can still resolve to its caller, but can no longer update the stores.

Thrown values and rejected promises are normalized to Error instances by mayfail.

Pass a readable store containing the operation when it needs to change after setup. execute reads the current operation from that store each time it runs.

License

MIT