Handle promise errors using second argument of then()

packages/microcosm/src/coroutine.js

@@ -35,7 +35,8 @@ export function coroutine(
   }
 
   if (isPromise(body)) {
-    body.then(action.complete).catch(action.error)
+    body.then(action.complete, action.error)
+
     return
   }
 

packages/microcosm/src/observable.js

@@ -263,28 +263,32 @@ function notifySubscription(subscription: *, type: *, value: *) {
   let observer = subscription._observer
 
   // This is what triggers subscription callbacks
-  switch (type) {
-    case NEXT:
-      observer.next(value)
-      break
-    case ERROR:
-      closeSubscription(subscription)
-      observer.error(value)
-      break
-    case COMPLETE:
-      closeSubscription(subscription)
-      observer.complete()
-      break
-    case CANCEL:
-      closeSubscription(subscription)
-      observer.cancel()
-      break
-    default:
-      assert(
-        false,
-        `Unrecognized type ${type}. This is an error internal to Microcosm. ` +
-          `Please file an issue: https://github.com/vigetlabs/microcosm/issues`
-      )
+  try {
+    switch (type) {
+      case NEXT:
+        observer.next(value)
+        break
+      case ERROR:
+        closeSubscription(subscription)
+        observer.error(value)
+        break
+      case COMPLETE:
+        closeSubscription(subscription)
+        observer.complete()
+        break
+      case CANCEL:
+        closeSubscription(subscription)
+        observer.cancel()
+        break
+      default:
+        assert(
+          false,
+          `Unrecognized type ${type}. This is an error internal to Microcosm. ` +
+            `Please file an issue: https://github.com/vigetlabs/microcosm/issues`
+        )
+    }
+  } catch (error) {
+    scheduler()._raise(error)
   }
 
   if (subscription.closed) {

packages/microcosm/src/scheduler.js

@@ -106,9 +106,7 @@ class Scheduler {
       this._errorCallbacks.forEach(callback => callback(error))
       this._errorCallbacks.length = 0
     } else {
-      setTimeout(() => {
-        throw error
-      }, 0)
+      throw error
     }
   }
 

packages/microcosm/src/subject.js

@@ -163,7 +163,7 @@ export class Subject extends Observable {
 function fromPromise(promise: Promise<*>): Subject {
   let subject = new Subject()
 
-  promise.then(subject.complete).catch(subject.error)
+  promise.then(subject.complete, subject.error)
 
   return subject
 }

packages/microcosm/test/helpers.js

@@ -11,3 +11,15 @@ export function asTree(history) {
 }
 
 export const delay = n => new Promise(resolve => setTimeout(resolve, n))
+
+export const withUniqueScheduler = () => {
+  let oldScheduler = global.__MICROCOSM_SCHEDULER__
+
+  beforeEach(function() {
+    global.__MICROCOSM_SCHEDULER__ = null
+  })
+
+  afterEach(function() {
+    global.__MICROCOSM_SCHEDULER__ = oldScheduler
+  })
+}

packages/microcosm/test/unit/middleware/promise-middleware.test.js

@@ -1,4 +1,5 @@
-import Microcosm from 'microcosm'
+import { Microcosm, scheduler } from 'microcosm'
+import { withUniqueScheduler } from '../../helpers'
 
 describe('Promise middleware', function() {
   it('completes when a promise resolves', async function() {
@@ -69,4 +70,50 @@ describe('Promise middleware', function() {
       expect(error).toBe('error')
     }
   })
+
+  describe('promise error trapping', () => {
+    withUniqueScheduler()
+
+    it('does not trap errors in domain handlers', async function() {
+      const repo = new Microcosm()
+      const onError = jest.fn()
+
+      repo.addDomain('test', {
+        register() {
+          return {
+            action: () => {
+              throw 'Oops'
+            }
+          }
+        }
+      })
+
+      scheduler().onError(onError)
+
+      await repo.push('action')
+
+      expect(onError).toHaveBeenCalledWith('Oops')
+    })
+
+    it('does not trap errors in effect handlers', async function() {
+      const repo = new Microcosm()
+      const onError = jest.fn()
+
+      repo.addEffect({
+        register() {
+          return {
+            action: () => {
+              throw 'Oops'
+            }
+          }
+        }
+      })
+
+      scheduler().onError(onError)
+
+      await repo.push('action')
+
+      expect(onError).toHaveBeenCalledWith('Oops')
+    })
+  })
 })