Assign function to event

Question

I have a class with a function that I want to assign to an event for a dgram obj.

MessageServer.prototype.OnBind = function (datagram) { var address = datagram.address(); console.log("server listening " + address.address + ":" + address.port); }; datagram.on("listening", function() { OnBind(this); });

I've tried:

The above, which OnBind is not defined
this.OnBind, which is not defined b/c this refers to the dgram
MessageServer.OnBind, which is not a function
datagram.on("listening",this.OnBind); but that doesnt pass in the dgram
datagram.on("listening",this.OnBind(this)); but that passes in the MessageServer

I'm guessing this is simple and I'm just being difficult... How do I assign the function to that event handler?

EDIT - THE FULL MODULE

var Dgram = require("dgram"); var MessageQueue = require("./MessageQueue"); var Message = require("./Message"); function MessageServer(name, listenPort, messageQueue, bindCallBack, messageReceiveCallBack,closeCallback,errorCallback) { this.Name = name; this.MessageQueue = messageQueue; this.Port = listenPort; var datagram = Dgram.createSocket("udp4"); MessageServer.prototype.Bind = function() { datagram.bind(this.Port); }; MessageServer.prototype.OnReceive = function(message, info) { var msg = new Message(message, info.address, info.port); MessageQueue.Add(msg); }; MessageServer.prototype.OnBind = function (datagram) { var address = datagram.address(); console.log("server listening " + address.address + ":" + address.port); }; datagram.on("listening",this.OnBind(datagram)); datagram.on("message", function(msg,info) { OnReceive(msg, info); }); datagram.on("error", function(err) { console.log(this.Name + " error: " + error); }); datagram.on("close", function() { console.log("server closing: " + Name); }); } module.exports = MessageServer;

Do not assign methods to the prototype in the constructor. This defies the point of assigning them to the prototype. — Willem D'Haeseleer
– Willem D'Haeseleer, Commented Jun 8, 2016 at 0:33
Hey thanks! Moved those functions out of the ctor and was able to get this moving. Rookie mistake! — Wjdavis5
– Wjdavis5, Commented Jun 8, 2016 at 0:51

Willem D'Haeseleer · Accepted Answer · 2016-06-08 00:45:49Z

Several issues with your code, Cleaned it up a little using the docs as reference.
See here: https://nodejs.org/api/dgram.html

Entirely off the cuff and untested off course. But it should give you an idea where to start I think.

MessageServer is a class here, Implement your logic in it's methods. Then instantiate it and call Bind to start it.
( Probably some room for improvement in this interface tough )

var myMessageServer = new MessageServer('MyServer', 8888, new MessageQueue(), etc...); myMessageServer.Bind();

-

var Dgram = require("dgram"); var Message = require("./Message"); function MessageServer(name, listenPort, messageQueue, bindCallBack, messageReceiveCallBack, closeCallback, errorCallback) { this.name = name; this.messageQueue = messageQueue; this.port = listenPort; this.server = Dgram.createSocket("udp4"); this.server.on("listening", this.OnBind.bind(this)); this.server.on("message", this.OnReceive.bind(this)); this.server.on("error", function (err) { console.log(this.name + " error: " + error); this.server.close(); }.bind(this)); this.server.on("close", function () { console.log("server closing: " + name); }); } MessageServer.prototype.Bind = function () { this.server.bind(this.port); }; MessageServer.prototype.OnReceive = function (message, info) { var msg = new Message(message, info.address, info.port); this.messageQueue.Add(msg); }; MessageServer.prototype.OnBind = function () { var address = this.server.address(); console.log("server listening " + address.address + ":" + address.port); }; module.exports = MessageServer;

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