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events: improve max listeners warning #27694

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events: improve max listeners warning #27694

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8 changes: 6 additions & 2 deletions lib/events.js
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,10 @@ const {
ERR_UNHANDLED_ERROR
} = require('internal/errors').codes;

const {
inspect
} = require('internal/util/inspect');

function EventEmitter() {
EventEmitter.init.call(this);
}
Expand Down Expand Up @@ -253,8 +257,8 @@ function _addListener(target, type, listener, prepend) {
// eslint-disable-next-line no-restricted-syntax
const w = new Error('Possible EventEmitter memory leak detected. ' +
`${existing.length} ${String(type)} listeners ` +
'added. Use emitter.setMaxListeners() to ' +
'increase limit');
`added to ${inspect(target, { depth: -1 })}. Use ` +
'emitter.setMaxListeners() to increase limit');
w.name = 'MaxListenersExceededWarning';
w.emitter = target;
w.type = type;
Expand Down
3 changes: 2 additions & 1 deletion test/parallel/test-event-emitter-max-listeners-warning-for-null.js
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ process.on('warning', common.mustCall((warning) => {
assert.strictEqual(warning.emitter, e);
assert.strictEqual(warning.count, 2);
assert.strictEqual(warning.type, null);
assert.ok(warning.message.includes('2 null listeners added.'));
assert.ok(warning.message.includes(
'2 null listeners added to [EventEmitter].'));
}));

e.on(null, () => {});
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3 changes: 2 additions & 1 deletion test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js
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Expand Up @@ -17,7 +17,8 @@ process.on('warning', common.mustCall((warning) => {
assert.strictEqual(warning.emitter, e);
assert.strictEqual(warning.count, 2);
assert.strictEqual(warning.type, symbol);
assert.ok(warning.message.includes('2 Symbol(symbol) listeners added.'));
assert.ok(warning.message.includes(
'2 Symbol(symbol) listeners added to [EventEmitter].'));
}));

e.on(symbol, () => {});
Expand Down
12 changes: 10 additions & 2 deletions test/parallel/test-event-emitter-max-listeners-warning.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,14 @@ const common = require('../common');
const events = require('events');
const assert = require('assert');

const e = new events.EventEmitter();
class FakeInput extends events.EventEmitter {
resume() {}
pause() {}
write() {}
end() {}
}

const e = new FakeInput();
e.setMaxListeners(1);

process.on('warning', common.mustCall((warning) => {
Expand All @@ -15,7 +22,8 @@ process.on('warning', common.mustCall((warning) => {
assert.strictEqual(warning.emitter, e);
assert.strictEqual(warning.count, 2);
assert.strictEqual(warning.type, 'event-type');
assert.ok(warning.message.includes('2 event-type listeners added.'));
assert.ok(warning.message.includes(
'2 event-type listeners added to [FakeInput].'));
}));

e.on('event-type', () => {});
Expand Down