Fix isDefaultPrevented and isPropagationStopped to not get nulled

gaearon · gaearon · commit 3c9768046eee · 2018-07-17T23:36:50.000+01:00
This was a bug introduced by #5947. It's very confusing that they become nulled while stopPropagation/preventDefault don't.
diff --git a/packages/events/SyntheticEvent.js b/packages/events/SyntheticEvent.js
@@ -70,6 +70,8 @@ function SyntheticEvent(
     delete this.nativeEvent;
     delete this.preventDefault;
     delete this.stopPropagation;
+    delete this.isDefaultPrevented;
+    delete this.isPropagationStopped;
   }
 
   this.dispatchConfig = dispatchConfig;
@@ -180,8 +182,8 @@ Object.assign(SyntheticEvent.prototype, {
     this.dispatchConfig = null;
     this._targetInst = null;
     this.nativeEvent = null;
-    this.isDefaultPrevented = null;
-    this.isPropagationStopped = null;
+    this.isDefaultPrevented = functionThatReturnsFalse;
+    this.isPropagationStopped = functionThatReturnsFalse;
     this._dispatchListeners = null;
     this._dispatchInstances = null;
     if (__DEV__) {
@@ -190,6 +192,16 @@ Object.assign(SyntheticEvent.prototype, {
         'nativeEvent',
         getPooledWarningPropertyDefinition('nativeEvent', null),
       );
+      Object.defineProperty(
+        this,
+        'isDefaultPrevented',
+        getPooledWarningPropertyDefinition('isDefaultPrevented', functionThatReturnsFalse),
+      );
+      Object.defineProperty(
+        this,
+        'isPropagationStopped',
+        getPooledWarningPropertyDefinition('isPropagationStopped', functionThatReturnsFalse),
+      );
       Object.defineProperty(
         this,
         'preventDefault',
diff --git a/packages/react-dom/src/events/__tests__/SyntheticEvent-test.js b/packages/react-dom/src/events/__tests__/SyntheticEvent-test.js
@@ -249,6 +249,58 @@ describe('SyntheticEvent', () => {
     expect(expectedCount).toBe(1);
   });
 
+  it('should warn when calling `isPropagationStopped` if the synthetic event has not been persisted', () => {
+    let node;
+    let expectedCount = 0;
+    let syntheticEvent;
+
+    const eventHandler = e => {
+      syntheticEvent = e;
+      expectedCount++;
+    };
+    node = ReactDOM.render(<div onClick={eventHandler} />, container);
+
+    const event = document.createEvent('Event');
+    event.initEvent('click', true, true);
+    node.dispatchEvent(event);
+
+    expect(() => expect(syntheticEvent.isPropagationStopped()).toBe(false)).toWarnDev(
+      'Warning: This synthetic event is reused for performance reasons. If ' +
+        "you're seeing this, you're accessing the method `isPropagationStopped` on a " +
+        'released/nullified synthetic event. This is a no-op function. If you must ' +
+        'keep the original synthetic event around, use event.persist(). ' +
+        'See https://fb.me/react-event-pooling for more information.',
+      {withoutStack: true},
+    );
+    expect(expectedCount).toBe(1);
+  });
+
+  it('should warn when calling `isDefaultPrevented` if the synthetic event has not been persisted', () => {
+    let node;
+    let expectedCount = 0;
+    let syntheticEvent;
+
+    const eventHandler = e => {
+      syntheticEvent = e;
+      expectedCount++;
+    };
+    node = ReactDOM.render(<div onClick={eventHandler} />, container);
+
+    const event = document.createEvent('Event');
+    event.initEvent('click', true, true);
+    node.dispatchEvent(event);
+
+    expect(() => expect(syntheticEvent.isDefaultPrevented()).toBe(false)).toWarnDev(
+      'Warning: This synthetic event is reused for performance reasons. If ' +
+        "you're seeing this, you're accessing the method `isDefaultPrevented` on a " +
+        'released/nullified synthetic event. This is a no-op function. If you must ' +
+        'keep the original synthetic event around, use event.persist(). ' +
+        'See https://fb.me/react-event-pooling for more information.',
+      {withoutStack: true},
+    );
+    expect(expectedCount).toBe(1);
+  });
+
   it('should properly log warnings when events simulated with rendered components', () => {
     let event;
     function assignEvent(e) {
