Node cli: --trace-warnings

‘--trace-warnings’ print stack traces for process warnings (including deprecations).

HelloWorld.js

var EventEmitter = require('events').EventEmitter;

EventEmitter.defaultMaxListeners = 3;

var emitter = new EventEmitter();

emitter.on('demo',() => {
 console.log("listener1");
});

emitter.on('demo',() => {
 console.log("listener2");
});

emitter.on('demo',() => {
 console.log("listener3");
});

emitter.on('demo',() => {
 console.log("listener4");
});

emitter.emit('demo')

Run HelloWorld.js using below command.

node --trace-warnings HelloWorld

You can see below kind of output.

listener1

listener2

listener3

listener4

(node:27700) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 4 demo listeners added. Use emitter.setMaxListeners() to increase limit

    at _addListener (events.js:243:17)

    at EventEmitter.addListener (events.js:259:10)

    at Object.<anonymous> (C:\Users\krishna\Documents\Study\nodejs\examples\HelloWorld.js:19:9)

    at Module._compile (internal/modules/cjs/loader.js:689:30)

    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)

    at Module.load (internal/modules/cjs/loader.js:599:32)

    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)

    at Function.Module._load (internal/modules/cjs/loader.js:530:3)

    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)

    at startup (internal/bootstrap/node.js:266:19)

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