How to properly remove event listeners in node js eventemitter

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)

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.