← Errors
Node.js emits this warning when more than 10 listeners (the default maximum) are added to a single event on an EventEmitter. It is a warning, not an error, designed to help detect potential memory leaks from forgotten listener removal.
Why it happens
- •Listeners are added in a loop or on every request without being removed.
- •A function that attaches a listener is called multiple times without cleanup.
- •Third-party libraries attach listeners to shared emitters without removing them.
Examples
JavaScript
Code that triggers the error
const EventEmitter = require("events");
const emitter = new EventEmitter();
for (let i = 0; i < 20; i++) {
emitter.on("data", () => console.log("received"));
}Error output
(node:12345) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 data listeners added to [EventEmitter]. Use emitter.setMaxListeners() to increase limit
How to fix it
Remove listeners when they are no longer needed with .off() or .removeListener(). Use .once() for one-shot listeners. If you genuinely need more than 10 listeners, call emitter.setMaxListeners(n). Treat the warning as a signal to review your listener lifecycle.
Fixed code
const EventEmitter = require("events");
const emitter = new EventEmitter();
function handleData() {
console.log("received");
}
emitter.on("data", handleData);
// When done:
emitter.off("data", handleData);Related errors
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