Using callback function in websocket api javascript

Question

i have a websocket client using the websocket api for javascript and my server is using socket.io

I'm trying to put a callback function like this

client js Using build in javascript WebSocket api

//im formatting the string like that because thats what socket.io needs for some reason
 var sendString = '42' + JSON.stringify(['checkLogin' , username, password])
 socket.send(sendString, function(returnData){
 console.log(returnData);
 resolve(returnData);
 })

but I keep getting an error that callback is not a function on my server-side using socket.io which looks like this

server js using socket.io library

socket.on('checkLogin', function(username, password, callback){
 console.log(username, password)
 webUser.findOne({username:username}, function(err, docs) {
 console.log(docs)
 if(docs){
 if(docs.password == password){
 callback(docs._id)
 }else{
 callback(false)
 }
 }
 if(!docs){
 callback(false)
 }
 });
})

what can i change to make this set the callback function correctly

• jfriend00: Which websocket library are you using? Please post a link to the NPM page for the exact webSocket library you're using.
• Nik Hendricks: I'm using the websocket API built into the browser. I'm testing it would in an HTML file but for building tabris apps it's uses the same api
• jfriend00: Server-side? You said the error is "callback is not a function" server-side so I'm asking what library you're using on the server. And, if you want help with a server-side error, you have to show us the relevant server-side code. If the error is not on your server, please correct your question.
• jfriend00: FYI, the client-side socket.send() does not have a callback function as an argument.
• Nik Hendricks: so is there no way to achieve what I'm trying to do using the WebSockets API ? also I edited my question sorry about that I'm not feeling right today :(

Answer 1

First problem. If you're using socket.io on the server-side, you must be using a socket.io client. You can't use a webSocket client with a socket.io server. They won't connection. This is true even though socket.io is using the webSocket transport underneath. A socket.io server needs the socket.io layer on top of webSocket.

Second problem, to send data with a socket.io client, you would use either socket.send() when you are just sending raw data with no message name or you would use socket.emit() when you are sending a message name.

In your case, I would recommend you use this on the client:

 socket.emit('checkLogin', {username, password}, function(result => {
 console.log(result);
 });

And, then modify your server code like this:

socket.on('checkLogin', function(data, callback){
 let username = data.username;
 let password = data.password;
 console.log(username, password)
 webUser.findOne({username:username}, function(err, docs) {
 console.log(docs)
 if(docs){
 if(docs.password == password){
 callback(docs._id)
 }else{
 callback(false)
 }
 }
 if(!docs){
 callback(false)
 }
 });
})

• Nik Hendricks: i can do regular things like socket.send('42' + JSON.stringify(['checkLogin' , username, password])); and it works fine just getting a callback to work would be weird at first i wasn't able to get them to connect but using this const socket = new WebSocket('ws://157.230.66.208:4343/socket.io/?EIO=3&transport=websocket','chat-protocol'); works like a charm
• jfriend00: @NicholasHendricks - If you're only going to use webSocket functionality, then use a webSocket server, not a socket.io server. The whole point of using socket.io is to use the features that it adds above and beyond a plain webSocket.
• Nik Hendricks: ok I was just wondering if it was possible the whole reason I'm using the WebSocket API is that Tabris.js uses it and cant be used with socket.io-client sadly thanks for all of your help
• jfriend00: @NicholasHendricks - If you want to program with webSocket, then change your server to a webSocket server and that will match with a webSocket client. You will be limited to the features that the standard webSocket protocol supports.
• Nik Hendricks: socket.io is already used for the web clients and i want to keep it that way that's why I was trying to make a solution for using pure WebSockets with the socket.io server because Tabris does not support socket.io client at all and now that I cant use callbacks or anything like that I definitely won't be using pure WebSockets unless I kind find a way to implement callbacks in some way. thanks for the help.