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Flarna wants to merge 3 commits into from
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events: allow monitoring error events #30932

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0a773db
events: allow monitoring error events
Flarna Dec 12, 2019
d156268
rename symbol
Flarna Dec 13, 2019
793205c
fix review findings
Flarna Dec 13, 2019
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fix review findings
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@Flarna
Flarna committed Dec 13, 2019
commit 793205c1f13767c004eeaab8fb94b0462d09e86b
6 changes: 3 additions & 3 deletions doc/api/events.md
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Expand Up @@ -160,7 +160,7 @@ by installing a listener using the symbol `errorMonitor`.

```js
const myEmitter = new MyEmitter();
myEmitter.on(errorMonitor, (err) => {
myEmitter.on(EventEmitter.errorMonitor, (err) => {
MyMonitoringTool.log(err);
});
myEmitter.emit('error', new Error('whoops!'));
Expand Down Expand Up @@ -365,11 +365,11 @@ Its `name` property is set to `'MaxListenersExceededWarning'`.
added: REPLACEME
-->

This symbol shall be used to install a listener only monitoring `'error'`
This symbol shall be used to install a listener for only monitoring `'error'`
events. Listeners installed using this symbol are called before the regular
`'error'` listeners are called.

Installing a listener using this symbol does not change the behavior once a
Installing a listener using this symbol does not change the behavior once an
`'error'` event is emitted, therefore the process will still crash if no
regular `'error'` listener is installed.

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13 changes: 4 additions & 9 deletions test/parallel/test-event-emitter-error-monitor.js
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Expand Up @@ -8,7 +8,9 @@ const theErr = new Error('MyError');

EE.on(
EventEmitter.errorMonitor,
common.mustCall((e) => assert.strictEqual(e, theErr), 3)
common.mustCall(function onErrorMonitor(e) {
assert.strictEqual(e, theErr);
}, 3)
);

// Verify with no error listener
Expand All @@ -23,14 +25,7 @@ EE.emit('error', theErr);

// Verify it works with once
process.nextTick(() => EE.emit('error', theErr));
async function testOnce() {
try {
await EventEmitter.once(EE, 'notTriggered');
} catch (e) {
assert.strictEqual(e, theErr);
}
}
testOnce();
assert.rejects(EventEmitter.once(EE, 'notTriggered'), theErr);

// Only error events trigger error monitor
EE.on('aEvent', common.mustCall());
Expand Down