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fix for issue 6887 #6893

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fix for issue 6887 #6893

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issue #6887: don't crash ensureScrollValueMonitoring when createEvent…
f0rk May 26, 2016
772e8e1
fint lint issues
f0rk May 26, 2016
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15 changes: 13 additions & 2 deletions src/renderers/dom/client/ReactBrowserEventEmitter.js
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Original file line number Diff line number Diff line change
Expand Up @@ -191,6 +191,13 @@ var ReactBrowserEventEmitter = Object.assign({}, ReactEventEmitterMixin, {
);
ReactBrowserEventEmitter.ReactEventListener = ReactEventListener;
},

/**
* @param {boolean} hasEventPageXY
*/
injectHasEventPageXY: function(val) {
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Instead of adding this method (which will end up in prod builds for no gain), let’s extract the if block contents into something like:

testEventPageXY: function() {
  if (document.createEvent) {
    hasEventPageXY = evt !== null && 'pageX' in evt;
  } else {
    hasEventPageXY = false;
  }
}

Then call this method both from ensureScrollValueMonitoring when if (hasEventPageXY === undefined) and from tests after stubbing out document.createElement.

hasEventPageXY = val;
},
},

/**
Expand Down Expand Up @@ -359,8 +366,12 @@ var ReactBrowserEventEmitter = Object.assign({}, ReactEventEmitterMixin, {
*/
ensureScrollValueMonitoring: function() {
if (hasEventPageXY === undefined) {
hasEventPageXY =
document.createEvent && 'pageX' in document.createEvent('MouseEvent');
if (document.createEvent) {
var evt = document.createEvent('MouseEvent');
hasEventPageXY = evt !== null && 'pageX' in evt;
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@gaearon gaearon Aug 26, 2016 •
edited
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This would need to be != null instead of !== null. If we’re protecting, let’s protect fully.

You will also need to add a note like

// Protect against document.createEvent() returning null
// Some popup blocker extensions appear to do this:
// https://github.com/facebook/react/issues/6887

} else {
hasEventPageXY = false;
}
}
if (!hasEventPageXY && !isMonitoringScrollValue) {
var refresh = ViewportMetrics.refreshScrollValues;
Expand Down
16 changes: 16 additions & 0 deletions src/renderers/dom/client/__tests__/ReactBrowserEventEmitter-test.js
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Expand Up @@ -110,6 +110,22 @@ describe('ReactBrowserEventEmitter', function() {
expect(LISTENER.mock.calls.length).toBe(1);
});

it('should not crash ensureScrollValueMonitoring when createEvent returns null', function() {
var originalCreateEvent = document.createEvent;
var mockedCreateEvent = jest.fn().mockImplementation(function() {
return null;
});
try {
document.createEvent = mockedCreateEvent;
ReactBrowserEventEmitter.injection.injectHasEventPageXY(undefined);
ReactBrowserEventEmitter.ensureScrollValueMonitoring();
} finally {
document.createEvent = originalCreateEvent;
}

expect(mockedCreateEvent.mock.calls.length).toBe(1);
});

it(
'should not invoke handlers if ReactBrowserEventEmitter is disabled',
function() {
Expand Down