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jasnell wants to merge 5 commits into from
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events: add async emitter.when #15204

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b10cea3
events: add async emitter.when
jasnell Sep 2, 2017
2888ab1
[Squash] Nits
jasnell Sep 5, 2017
c02d332
[Squash] Use Error for reason
jasnell Sep 5, 2017
efd97d2
[Squash] Add error code to docs
jasnell Sep 5, 2017
438e695
[Squash] Remove prepend option
jasnell Sep 5, 2017
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[Squash] Remove prepend option
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@jasnell
jasnell committed Sep 5, 2017
commit 438e69510f2558fe74e2deb3939c718b5a0b7fcd
5 changes: 1 addition & 4 deletions doc/api/events.md
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Expand Up @@ -586,15 +586,12 @@ to indicate an unlimited number of listeners.

Returns a reference to the `EventEmitter`, so that calls can be chained.

### async emitter.when(eventName[, options])
### async emitter.when(eventName)
<!-- YAML
added: REPLACEME
-->

* `eventName` {any} The name of the event.
* `options` {Object}
* `prepend` {boolean} True to prepend the handler used to resolve the
`Promise` to the handler queue.
* Returns: {Promise}

Creates and returns a `Promise` that is resolved with a one-time event handler.
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17 changes: 3 additions & 14 deletions lib/events.js
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Expand Up @@ -375,13 +375,7 @@ EventEmitter.prototype.prependOnceListener =
// An awaitable one-time event listener. Registers a once handler and
// returns an associated promise.
EventEmitter.prototype.when =
function when(type, options = { prepend: false }) {
if (options == null || typeof options !== 'object') {
// This must be lazy evaluated
const errors = lazyErrors();
throw new errors.TypeError('ERR_INVALID_ARG_TYPE',
'options', 'object');
}
function when(type) {
lazyPromiseBinding();
const promise = createPromise();
let resolved = false;
Expand All @@ -407,13 +401,8 @@ EventEmitter.prototype.when =
// Do not use once because it will trigger a removeListener *before*
// the promise is resolved, which throws off the cancel logic when
// removeListener is called.
if (options.prepend) {
this.prependListener(type, listener);
this.prependListener('removeListener', cancel);
} else {
this.on(type, listener);
this.on('removeListener', cancel);
}
this.on(type, listener);
this.on('removeListener', cancel);
return promise;
};

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17 changes: 0 additions & 17 deletions test/parallel/test-event-emitter-when.js
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Expand Up @@ -18,23 +18,6 @@ const ee = new EventEmitter();
assert.strictEqual(ee.listenerCount('foo'), 0);
}

{
let a = 1;
ee.when('foo')
.then(common.mustCall(() => {
assert.strictEqual(a, 2);
}))
.catch(common.mustNotCall());

ee.when('foo', { prepend: true })
.then(common.mustCall(() => {
assert.strictEqual(a++, 1);
}))
.catch(common.mustNotCall());

ee.emit('foo');
}

{
ee.when('foo')
.then(common.mustCall(() => {
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