javascriptnode.jsexpresseventemitterevent-stream

How to properly remove event listeners in node js eventemitter


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(){
            //
        })
    })

})

Solution

  • 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.