Correctly use falsy outputs (#4768)

statelyai · Feb 27, 2024 · 4a29f8a · 4a29f8a
1 parent b421ab9
commit 4a29f8a
Show file tree

Hide file tree

Showing 4 changed files with 55 additions and 5 deletions.
diff --git a/.changeset/nasty-foxes-move.md b/.changeset/nasty-foxes-move.md
@@ -0,0 +1,5 @@
+---
+'xstate': patch
+---
+
+Correctly use falsy outputs (instead of accidentally converting them to `undefined`).
diff --git a/packages/core/src/StateMachine.ts b/packages/core/src/StateMachine.ts
@@ -152,9 +152,9 @@ export class StateMachine<
 
     if (
       isDevelopment &&
-      !this.root.output &&
+      !('output' in this.root) &&
       Object.values(this.states).some(
-        (state) => state.type === 'final' && !!state.output
+        (state) => state.type === 'final' && 'output' in state
       )
     ) {
       console.warn(

diff --git a/packages/core/src/stateUtils.ts b/packages/core/src/stateUtils.ts
@@ -1063,12 +1063,12 @@ function getMachineOutput(
   rootNode: AnyStateNode,
   rootCompletionNode: AnyStateNode
 ) {
-  if (!rootNode.output) {
+  if (rootNode.output === undefined) {
     return;
   }
   const doneStateEvent = createDoneStateEvent(
     rootCompletionNode.id,
-    rootCompletionNode.output && rootCompletionNode.parent
+    rootCompletionNode.output !== undefined && rootCompletionNode.parent
       ? resolveOutput(
           rootCompletionNode.output,
           snapshot.context,
@@ -1158,7 +1158,7 @@ function enterStates(
         internalQueue.push(
           createDoneStateEvent(
             parent!.id,
-            stateNodeToEnter.output
+            stateNodeToEnter.output !== undefined
               ? resolveOutput(
                   stateNodeToEnter.output,
                   nextSnapshot.context,

diff --git a/packages/core/test/final.test.ts b/packages/core/test/final.test.ts
@@ -1241,4 +1241,49 @@ describe('final states', () => {
     // if `xstate.done.actor.*` would be delivered first the value would be `completed`
     expect(actorRef.getSnapshot().value).toBe('canceled');
   });
+
+  it('should be possible to complete with a null output (directly on root)', () => {
+    const machine = createMachine({
+      initial: 'start',
+      states: {
+        start: {
+          on: {
+            NEXT: 'end'
+          }
+        },
+        end: {
+          type: 'final'
+        }
+      },
+      output: null
+    });
+
+    const actorRef = createActor(machine).start();
+    actorRef.send({ type: 'NEXT' });
+
+    expect(actorRef.getSnapshot().output).toBe(null);
+  });
+
+  it("should be possible to complete with a null output (resolving with final state's output)", () => {
+    const machine = createMachine({
+      initial: 'start',
+      states: {
+        start: {
+          on: {
+            NEXT: 'end'
+          }
+        },
+        end: {
+          type: 'final',
+          output: null
+        }
+      },
+      output: ({ event }) => event.output
+    });
+
+    const actorRef = createActor(machine).start();
+    actorRef.send({ type: 'NEXT' });
+
+    expect(actorRef.getSnapshot().output).toBe(null);
+  });
 });