Merge pull request #311 from laszlopandy/fix-fromPromise-from-pending…

…-promise

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 6.0.6
+
+* [fromPromise carries forward old value from pending observable](https://github.com/mobxjs/mobx-utils/pull/311)
+
+# 6.0.5
+
 # 6.0.4
 
 * [ObservableGroupMap.ts: remove console.log #289](https://github.com/mobxjs/mobx-utils/pull/289)

src/from-promise.ts

@@ -181,10 +181,9 @@ export function fromPromise<T>(
 
     promise.isPromiseBasedObservable = true
     promise.case = caseImpl
+    const oldState = oldPromise ? (oldPromise as any).state : undefined
     const oldData =
-        oldPromise && (oldPromise as any).state === FULFILLED
-            ? (oldPromise as any).value
-            : undefined
+        oldState === FULFILLED || oldState === PENDING ? (oldPromise as any).value : undefined
     extendObservable(
         promise,
         {

test/from-promise.js

@@ -38,18 +38,20 @@ test("old state is undefined", (done) => {
     )
 })
 
-test("resolves old state", (done) => {
-    const oldP = utils.fromPromise(new Promise((resolve) => resolve(9)))
-    mobx.when(
-        () => oldP.state == "fulfilled",
-        () => {
-            const p = new Promise((resolve) => resolve(7))
-            const obs = utils.fromPromise(p, oldP)
-            expect(obs.value).toBe(9)
-            expect(obs.state).toBe("pending")
-            done()
-        }
-    )
+test("resolves old state", () => {
+    let obs = utils.fromPromise.resolve(9)
+    expect(obs.value).toBe(9)
+    expect(obs.state).toBe("fulfilled")
+
+    // Expect old state to be carried forward from fulfilled observable
+    obs = utils.fromPromise(Promise.resolve(7), obs)
+    expect(obs.value).toBe(9)
+    expect(obs.state).toBe("pending")
+
+    // Expect old state to be carried forward from *pending* observable
+    obs = utils.fromPromise(Promise.resolve(10), obs)
+    expect(obs.value).toBe(9)
+    expect(obs.state).toBe("pending")
 })
 
 test("resolves new state", (done) => {