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Disable ViewportMetrics unless MouseEvent lacks support for pageX/pageY #2271

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Disable ViewportMetrics unless MouseEvent lacks support for pageX/pageY #2271

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10 changes: 9 additions & 1 deletion src/browser/ReactBrowserEventEmitter.js
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,7 @@ var merge = require('merge');
* React Core . General Purpose Event Plugin System
*/

var hasEventPageXY;
var alreadyListeningTo = {};
var isMonitoringScrollValue = false;
var reactTopListenersCounter = 0;
Expand Down Expand Up @@ -331,12 +332,19 @@ var ReactBrowserEventEmitter = merge(ReactEventEmitterMixin, {
* Listens to window scroll and resize events. We cache scroll values so that
* application code can access them without triggering reflows.
*
* ViewportMetrics is only used by SyntheticMouse/TouchEvent and only when
* pageX/pageY isn't supported (legacy browsers).
*
* NOTE: Scroll events do not bubble.
*
* @see http://www.quirksmode.org/dom/events/scroll.html
*/
ensureScrollValueMonitoring: function(){
if (!isMonitoringScrollValue) {
if (hasEventPageXY === undefined) {
hasEventPageXY =
document.createEvent && 'pageX' in document.createEvent('MouseEvent');
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I think @petehunt's plan was that we'd only access the DOM in files in src/browser/ui/ – but maybe ReactBrowserEventEmitter should be moved there?

}
if (!hasEventPageXY && !isMonitoringScrollValue) {
var refresh = ViewportMetrics.refreshScrollValues;
ReactBrowserEventEmitter.ReactEventListener.monitorScrollValue(refresh);
isMonitoringScrollValue = true;
Expand Down