fix: Add child_changed listener and tests.

src/__tests__/to-map.test.ts

@@ -21,7 +21,7 @@ describe("toMap", () => {
     config: config.client,
     firebase
   });
-  afterAll(async () => {
+  afterEach(async () => {
     const ref = getFirebaseRef({ firebase, path: `${testPath}` });
     await ref.set(null);
   });
@@ -101,4 +101,36 @@ Object {
     expect(toJS(map)).toMatchInlineSnapshot(`Object {}`);
     unsub();
   });
+  test("works with child_changed", async () => {
+    const ref = getFirebaseRef({ firebase, path: testPath });
+    const { value: map } = toMap(ref);
+    await ref.set(listAsObject);
+    expect(toJS(map)).toMatchInlineSnapshot(`
+Object {
+  "id_0": Object {
+    "data": 0,
+  },
+  "id_1": Object {
+    "data": 1,
+  },
+}
+`);
+    await firebase
+      .database()
+      .ref(testPath + "/id_0")
+      .update({ NEW: "DATA" });
+    expect(toJS(map)).toMatchInlineSnapshot(`
+Object {
+  "id_0": Object {
+    "NEW": "DATA",
+    "data": 0,
+  },
+  "id_1": Object {
+    "data": 1,
+  },
+}
+`);
+    await ref.set({});
+    expect(toJS(map)).toMatchInlineSnapshot(`Object {}`);
+  });
 });

src/to-map.ts

@@ -62,9 +62,27 @@ export function toMap<K, V>(
     }
     map.delete(currentMapKey);
   });
+  const unsubChildChanged = ref.on("child_changed", (v: any) => {
+    const valueOrNull = !v ? null : v.val();
+    const keyOrNull = !v ? null : v.key;
+    const currentMapKey = mapKey(keyOrNull);
+    const currentMapValue = mapValue(valueOrNull);
+    if (!map.has(currentMapKey)) {
+      map.set(currentMapKey, observable.box(currentMapValue));
+      return;
+    }
+
+    const previousMapValue = map.get(currentMapKey).get();
+    const shouldUpdateValue = filter(previousMapValue, currentMapValue);
+    if (!shouldUpdateValue) {
+      return;
+    }
+    map.get(currentMapKey).set(currentMapValue);
+  });
   const unsub = () => {
     unsubChildAdded && unsubChildAdded();
     unsubChildRemoved && unsubChildRemoved();
+    unsubChildChanged && unsubChildChanged();
   };
 
   return { value: map, unsub };