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Test Info:

<!DOCTYPE html>
<title>Synthetic events are always cancelable by default</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
const eventsMap = {
wheel: 'WheelEvent',
mousewheel: 'WheelEvent',
touchstart: 'TouchEvent',
touchmove: 'TouchEvent',
touchend: 'TouchEvent',
touchcancel: 'TouchEvent',
}
function isCancelable(eventName, interfaceName) {
test(() => {
assert_implements(interfaceName in self, `${interfaceName} should be supported`);
let defaultPrevented = null;
addEventListener(eventName, event => {
event.preventDefault();
defaultPrevented = event.defaultPrevented;
});
const event = new self[interfaceName](eventName);
assert_false(event.cancelable, 'cancelable');
const dispatchEventReturnValue = dispatchEvent(event);
assert_false(defaultPrevented, 'defaultPrevented');
assert_true(dispatchEventReturnValue, 'dispatchEvent() return value');
}, `Synthetic ${eventName} event with interface ${interfaceName} is not cancelable`);
}
for (const eventName in eventsMap) {
isCancelable(eventName, eventsMap[eventName]);
isCancelable(eventName, 'Event');
}
</script>