mapAsync

The mapAsync operator transforms each value from a source into an asynchronous operation,
returning a state-like value that tracks loading, success, or error.

---

✅ Basic usage

import { event } from "signux";
import { mapAsync } from "signux/operators";

const query = event<string>();
const results = query.pipe(
  mapAsync(async (term) => {
    const res = await fetch("/search?q=" + term);
    return res.json();
  }),
);

---

🔁 Result format

Each emission from mapAsync is an object with one of the following shapes:

{
  loading: true;
  data: never;
  error: never;
}
{
  loading: false;
  data: T;
  error: never;
}
{
  loading: false;
  data: never;
  error: E;
}

This pattern is compatible with stateAsync(...).

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⚙️ How it works

When the source emits a value:

1. mapAsync triggers the async function
2. It emits a loading state
3. Then either a success or error state

If multiple async calls are made in a row, only the latest one is kept.

---

🧩 Use cases

• Fetching suggestions from input
• Handling async side-effects in pipes
• Replacing stateAsync() with finer control

---

📦 Signature

function mapAsync<T, R>(
  fn: (value: T) => Promise<R>,
): OperatorFn<T, AsyncStateValue<R>>;