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fix: Use passive event listeners for touchstart/touchmove (#4440)

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If passive event listening is supported, we should use it.

Fixes #4432.
This commit is contained in:
mister-ben 2017-06-28 07:36:06 +01:00 committed by Gary Katsevman
parent b63666379d
commit b4dc4f85b0
1 changed files with 34 additions and 1 deletions
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35
src/js/utils/events.js
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@ -202,6 +202,33 @@ export function fixEvent(event) {
return event;
}
/**
* Whether passive event listeners are supported
*/
let _supportsPassive = false;
(function() {
try {
const opts = Object.defineProperty({}, 'passive', {
get() {
_supportsPassive = true;
}
});
window.addEventListener('test', null, opts);
} catch (e) {
// disregard
}
})();
/**
* Touch events Chrome expects to be passive
*/
const passiveEvents = [
'touchstart',
'touchmove'
];
/**
* Add an event listener to element
* It stores the handler function in a separate cache object
@ -273,7 +300,13 @@ export function on(elem, type, fn) {
if (data.handlers[type].length === 1) {
if (elem.addEventListener) {
elem.addEventListener(type, data.dispatcher, false);
let options = false;
if (_supportsPassive &&
passiveEvents.indexOf(type) > -1) {
options = {passive: true};
}
elem.addEventListener(type, data.dispatcher, options);
} else if (elem.attachEvent) {
elem.attachEvent('on' + type, data.dispatcher);
}