Added mapCompleted

packages/signals/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@holochain-open-dev/signals",
-  "version": "0.300.0-dev.4",
+  "version": "0.300.0-dev.5",
   "description": "Holochain async-signals to build reusable holochain-open-dev modules",
   "author": "[email protected]",
   "main": "dist/index.js",

packages/signals/src/index.ts

@@ -16,3 +16,4 @@ export * from "./join-map.js";
 export * from "./utils.js";
 export * from "./holochain.js";
 export * from "./watch.js";
+export * from "./map-completed.js";

packages/signals/src/map-completed.ts

@@ -0,0 +1,21 @@
+import { AsyncComputed, AsyncSignal } from "async-signals";
+
+/**
+ * Transforms the value for the given signal, when its status is 'completed'.
+ *
+ * When the status of the given `AsyncSignal` is other than 'completed', it returns that result.
+ */
+export function mapCompleted<T, U>(
+  asyncSignal: AsyncSignal<T>,
+  mapFn: (value: T) => U
+): AsyncSignal<U> {
+  return new AsyncComputed(() => {
+    const result = asyncSignal.get();
+    if (result.status !== "completed") return result;
+    const value = mapFn(result.value);
+    return {
+      status: "completed",
+      value,
+    };
+  });
+}

packages/signals/tests/map-completed.test.js

@@ -0,0 +1,23 @@
+import { expect, it } from "vitest";
+import { fromPromise } from "async-signals";
+
+import { mapCompleted, watch } from "../src";
+
+const sleep = (ms) => new Promise((r) => setTimeout(() => r(), ms));
+
+it("mapCompleted", async () => {
+  const signal = fromPromise(async () => {
+    await sleep(10);
+    return 1;
+  });
+  const signal2 = mapCompleted(signal, (n) => n + 1);
+
+  watch(signal2, () => {});
+
+  expect(signal2.get().status).to.be.equal("pending");
+
+  await sleep(20);
+
+  expect(signal2.get().status).to.be.equal("completed");
+  expect(signal2.get().value).to.be.equal(2);
+});