How to properly remove event listeners in node js eventemitter

Question

I have a set up with a GET and a POST route, the idea being that POSTing to the route triggers an event, and the GET route is a server-sent eventstream which fires each time the POSTed event is triggered... however, i think i've done something wrong as event listeners seem to get added routinely despite only having one event stream subscriber... what am i doing wrong?

var events = require('events'),
EventEmitter = events.EventEmitter,
rr = new EventEmitter();

app.post('/api/:boardname/remoterefresh', function(req, res){
    var boardname = req.param('boardname'),
    data = new Date().getTime();
    rr.emit("refresh-"+boardname, data)
    res.json({data: data})
});

app.get('/api/:boardname/remoterefresh', function(req, res){
    var boardname = req.param('boardname')

    rr.on("refresh-"+boardname, function(data){
        setTimeout(function(){
            res.write('data: '+data+'\n\n');
        }, 1000)
    });

    req.socket.setTimeout(Infinity);

    res.writeHead(200, {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive'
    });

    res.write('\n');

    req.on('close', function(){
        console.log('closed')
        rr.removeListener("refresh-"+boardname, function(){
            //
        })
    })

})

possible duplicate of [Unbinding events in Node.js](http://stackoverflow.com/questions/4305175/unbinding-events-in-node-js) — Farid Nouri Neshat, May 27 '14 at 16:01
Could this cause a race condition and leak data across requests? — Charlie Schliesser, Aug 27 '14 at 02:52

score 59 · Accepted Answer · answered May 27 '14 at 16:00

You should name the function you attach as event handler. Then on removing it, you just pass the function by name:

app.get('/api/:boardname/remoterefresh', function(req, res){
    var boardname = req.param('boardname')
    function refreshHandler(data){
        setTimeout(function(){
            res.write('data: '+data+'\n\n');
        }, 1000)
    }
    rr.on("refresh-"+boardname, refreshHandler);

    req.socket.setTimeout(Infinity);

    res.writeHead(200, {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive'
    });

    res.write('\n');

    req.on('close', function(){
        console.log('closed')
        rr.removeListener("refresh-"+boardname, refreshHandler);
    });
});

Basically removeListener will look up the given function by reference, if it found that function it will remove it from the event hander.

thanks man. you are the life saver :) it was joke. but I found solution of my problem — SefaUn, Jul 03 '22 at 13:38

score 7 · Answer 2 · edited Feb 27 '21 at 15:15

7

To avoid referencing the anonymous listener callback function, you can dangerously wipe registered listeners with the emitter.removeAllListeners method:

rr.removeAllListeners("refresh-"+boardname)

Be aware that this approach can easily result in unintended side-effects (deregistering listeners registered elsewhere in the codebase), and should be reserved for "wipe the slate clean" use cases (eg: Testing)

edited Feb 27 '21 at 15:15

Patrick Fowler

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answered Sep 05 '19 at 00:37

goodhyun

4,814
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2

note that `rr.removeAllListeners` (in the plural) is the correct name – Gershom Maes Oct 18 '19 at 21:30
I also found I needed to use removeAllListeners, when removeListener didn't seem to recognise a method name inside a class which was also bound with function.bind(this), so perhaps that doesn't work. – scipilot May 02 '20 at 03:49

How to properly remove event listeners in node js eventemitter

2 Answers2

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