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test(() => {
const target = new EventTarget();
assert_implements(target.on, "The EventTarget interface has an `on` method");
assert_equals(typeof target.on, "function",
"EventTarget should have the on method");
const testEvents = target.on("test");
assert_true(testEvents instanceof Observable,
"EventTarget.on returns an Observable");
const results = [];
testEvents.subscribe({
next: value => results.push(value),
error: () => results.push("error"),
complete: () => results.push("complete"),
});
assert_array_equals(results, [],
"Observable does not emit events until event is fired");
const event = new Event("test");
target.dispatchEvent(event);
assert_array_equals(results, [event]);
target.dispatchEvent(event);
assert_array_equals(results, [event, event]);
}, "EventTarget.on() returns an Observable");
test(() => {
const target = new EventTarget();
const testEvents = target.on("test");
const ac = new AbortController();
const results = [];
testEvents.subscribe({
next: (value) => results.push(value),
error: () => results.push('error'),
complete: () => results.complete('complete'),
}, { signal: ac.signal });
assert_array_equals(results, [],
"Observable does not emit events until event is fired");
const event1 = new Event("test");
const event2 = new Event("test");
const event3 = new Event("test");
target.dispatchEvent(event1);
target.dispatchEvent(event2);
assert_array_equals(results, [event1, event2]);
ac.abort();
target.dispatchEvent(event3);
assert_array_equals(results, [event1, event2],
"Aborting the subscription removes the event listener and stops the " +
"emission of events");
}, "Aborting the subscription should stop the emission of events");
test(() => {
const target = new EventTarget();
const testEvents = target.on("test");
const results = [];
testEvents.subscribe(e => results.push(e));
testEvents.subscribe(e => results.push(e));
const event1 = new Event("test");
const event2 = new Event("test");
target.dispatchEvent(event1);
target.dispatchEvent(event2);
assert_array_equals(results, [event1, event1, event2, event2]);
}, "EventTarget Observables can multicast subscriptions for event handling");
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