facebook · necolas · Sep 10, 2019 · Sep 6, 2019
diff --git a/packages/react-events/src/dom/Tap.js b/packages/react-events/src/dom/Tap.js
@@ -21,29 +21,33 @@ import {
   isMac,
   dispatchDiscreteEvent,
   dispatchUserBlockingEvent,
+  getTouchById,
+  hasModifierKey,
 } from './shared';
 
-type TapProps = {|
-  disabled: boolean,
-  preventDefault: boolean,
-  onTapCancel: (e: TapEvent) => void,
-  onTapChange: boolean => void,
-  onTapEnd: (e: TapEvent) => void,
-  onTapStart: (e: TapEvent) => void,
-  onTapUpdate: (e: TapEvent) => void,
-|};
-
-type TapState = {
+type TapProps = $ReadOnly<{|
+  disabled?: boolean,
+  maximumDistance?: number,
+  preventDefault?: boolean,
+  onTapCancel?: (e: TapEvent) => void,
+  onTapChange?: boolean => void,
+  onTapEnd?: (e: TapEvent) => void,
+  onTapStart?: (e: TapEvent) => void,
+  onTapUpdate?: (e: TapEvent) => void,
+|}>;
+
+type TapState = {|
   activePointerId: null | number,
   buttons: 0 | 1 | 4,
   gestureState: TapGestureState,
   ignoreEmulatedEvents: boolean,
+  initialPosition: {|x: number, y: number|},
   isActive: boolean,
   pointerType: PointerType,
   responderTarget: null | Element,
   rootEvents: null | Array<string>,
   shouldPreventClick: boolean,
-};
+|};
 
 type TapEventType =
   | 'tap-cancel'
@@ -76,10 +80,10 @@ type TapGestureState = {|
   y: number,
 |};
 
-type TapEvent = {|
+type TapEvent = $ReadOnly<{|
   ...TapGestureState,
   type: TapEventType,
-|};
+|}>;
 
 /**
  * Native event dependencies
@@ -120,6 +124,7 @@ function createInitialState(): TapState {
     buttons: 0,
     ignoreEmulatedEvents: false,
     isActive: false,
+    initialPosition: {x: 0, y: 0},
     pointerType: '',
     responderTarget: null,
     rootEvents: null,
@@ -299,23 +304,6 @@ function removeRootEventTypes(
  * Managing pointers
  */
 
-function getTouchById(
-  nativeEvent: TouchEvent,
-  pointerId: null | number,
-): null | Touch {
-  if (pointerId != null) {
-    const changedTouches = nativeEvent.changedTouches;
-    for (let i = 0; i < changedTouches.length; i++) {
-      const touch = changedTouches[i];
-      if (touch.identifier === pointerId) {
-        return touch;
-      }
-    }
-    return null;
-  }
-  return null;
-}
-
 function getHitTarget(
   event: ReactDOMResponderEvent,
   context: ReactDOMResponderContext,
@@ -362,14 +350,6 @@ function isActivePointer(
   }
 }
 
-function isModifiedTap(event: ReactDOMResponderEvent): boolean {
-  const nativeEvent: any = event.nativeEvent;
-  const {altKey, ctrlKey, metaKey, shiftKey} = nativeEvent;
-  return (
-    altKey === true || ctrlKey === true || metaKey === true || shiftKey === true
-  );
-}
-
 function shouldActivate(event: ReactDOMResponderEvent): boolean {
   const nativeEvent: any = event.nativeEvent;
   const pointerType = event.pointerType;
@@ -511,7 +491,12 @@ const responderImpl = {
           state.pointerType = event.pointerType;
           state.responderTarget = context.getResponderNode();
           state.shouldPreventClick = props.preventDefault !== false;
-          state.gestureState = createGestureState(context, props, state, event);
+
+          const gestureState = createGestureState(context, props, state, event);
+          state.gestureState = gestureState;
+          state.initialPosition.x = gestureState.x;
+          state.initialPosition.y = gestureState.y;
+
           dispatchStart(context, props, state);
           dispatchChange(context, props, state);
           addRootEventTypes(rootEventTypes, context, state);
@@ -549,7 +534,26 @@ const responderImpl = {
 
         if (state.isActive && isActivePointer(event, state)) {
           state.gestureState = createGestureState(context, props, state, event);
-          if (context.isTargetWithinResponder(hitTarget)) {
+          let shouldUpdate = true;
+
+          if (!context.isTargetWithinResponder(hitTarget)) {
+            shouldUpdate = false;
+          } else if (
+            props.maximumDistance != null &&
+            props.maximumDistance >= 10
+          ) {
+            const maxDistance = props.maximumDistance;
+            const initialPosition = state.initialPosition;
+            const currentPosition = state.gestureState;
+            const moveX = initialPosition.x - currentPosition.x;
+            const moveY = initialPosition.y - currentPosition.y;
+            const moveDistance = Math.sqrt(moveX * moveX + moveY * moveY);
+            if (moveDistance > maxDistance) {
+              shouldUpdate = false;
+            }
+          }
+
+          if (shouldUpdate) {
             dispatchUpdate(context, props, state);
           } else {
             state.isActive = false;
@@ -575,7 +579,7 @@ const responderImpl = {
 
           if (context.isTargetWithinResponder(hitTarget)) {
             // Determine whether to call preventDefault on subsequent native events.
-            if (isModifiedTap(event)) {
+            if (hasModifierKey(event)) {
               state.shouldPreventClick = false;
             }
             dispatchEnd(context, props, state);

diff --git a/packages/react-events/src/dom/__tests__/Tap-test.internal.js b/packages/react-events/src/dom/__tests__/Tap-test.internal.js
@@ -139,6 +139,60 @@ describeWithPointerEvent('Tap responder', hasPointerEvents => {
     });
   });
 
+  describe('maximumDistance', () => {
+    let onTapCancel, onTapUpdate, ref;
+
+    function render(props) {
+      const Component = () => {
+        const listener = useTap(props);
+        return <div ref={ref} listeners={listener} />;
+      };
+      ReactDOM.render(<Component />, container);
+      document.elementFromPoint = () => ref.current;
+    }
+
+    beforeEach(() => {
+      onTapCancel = jest.fn();
+      onTapUpdate = jest.fn();
+      ref = React.createRef();
+      render({
+        maximumDistance: 20,
+        onTapCancel,
+        onTapUpdate,
+      });
+    });
+
+    test('ignores values less than 10', () => {
+      render({
+        maximumDistance: 5,
+        onTapCancel,
+        onTapUpdate,
+      });
+      const target = createEventTarget(ref.current);
+      const pointerType = 'mouse';
+      target.pointerdown({pointerType, x: 0, y: 0});
+      target.pointermove({pointerType, x: 10, y: 10});
+      expect(onTapUpdate).toHaveBeenCalledTimes(1);
+      expect(onTapCancel).toHaveBeenCalledTimes(0);
+    });
+
+    testWithPointerType('below threshold', pointerType => {
+      const target = createEventTarget(ref.current);
+      target.pointerdown({pointerType, x: 0, y: 0});
+      target.pointermove({pointerType, x: 10, y: 10});
+      expect(onTapUpdate).toHaveBeenCalledTimes(1);
+      expect(onTapCancel).toHaveBeenCalledTimes(0);
+    });
+
+    testWithPointerType('above threshold', pointerType => {
+      const target = createEventTarget(ref.current);
+      target.pointerdown({pointerType, x: 0, y: 0});
+      target.pointermove({pointerType, x: 15, y: 14});
+      expect(onTapUpdate).toHaveBeenCalledTimes(0);
+      expect(onTapCancel).toHaveBeenCalledTimes(1);
+    });
+  });
+
   describe('onTapStart', () => {
     let onTapStart, ref;
 
@@ -496,15 +550,16 @@ describeWithPointerEvent('Tap responder', hasPointerEvents => {
   });
 
   describe('onTapCancel', () => {
-    let onTapCancel, parentRef, ref, siblingRef;
+    let onTapCancel, onTapUpdate, parentRef, ref, siblingRef;
 
     beforeEach(() => {
       onTapCancel = jest.fn();
+      onTapUpdate = jest.fn();
       parentRef = React.createRef();
       ref = React.createRef();
       siblingRef = React.createRef();
       const Component = () => {
-        const listener = useTap({onTapCancel});
+        const listener = useTap({onTapCancel, onTapUpdate});
         return (
           <div ref={parentRef}>
             <div ref={ref} listeners={listener} />
@@ -546,6 +601,8 @@ describeWithPointerEvent('Tap responder', hasPointerEvents => {
           y: 0,
         }),
       );
+      target.pointermove({pointerType, x: 5, y: 5});
+      expect(onTapUpdate).not.toBeCalled();
     });
 
     test('long press context menu', () => {

diff --git a/packages/react-events/src/dom/shared/index.js b/packages/react-events/src/dom/shared/index.js
@@ -45,3 +45,28 @@ export function dispatchUserBlockingEvent(
 ) {
   context.dispatchEvent(payload, callback, UserBlockingEvent);
 }
+
+export function getTouchById(
+  nativeEvent: TouchEvent,
+  pointerId: null | number,
+): null | Touch {
+  if (pointerId != null) {
+    const changedTouches = nativeEvent.changedTouches;
+    for (let i = 0; i < changedTouches.length; i++) {
+      const touch = changedTouches[i];
+      if (touch.identifier === pointerId) {
+        return touch;
+      }
+    }
+    return null;
+  }
+  return null;
+}
+
+export function hasModifierKey(event: ReactDOMResponderEvent): boolean {
+  const nativeEvent: any = event.nativeEvent;
+  const {altKey, ctrlKey, metaKey, shiftKey} = nativeEvent;
+  return (
+    altKey === true || ctrlKey === true || metaKey === true || shiftKey === true
+  );
+}