Voice of a Developer: Javascript WebSocket

Disadvantages of WebSocket

Open connection

The disadvantage is that it keeps the connection open on the server for the duration of the time user is interacting with the page. Therefore, it consumes more resources on the server.
Single-channel communication

If your app does not need too much duplex communication with the server then you can think of using other approaches like long polling, AJAX over WebSocket.

WebSocket server

I suggest to use /download any server supporting WebSocket. In IIS, you can also enable WebSocket via adding Application Development features. For testing, I want to use WebSocket servers like UNIX.

Steps to run the server

Download WebSocketd from URL.
Extract the zip file in a folder like C:\websocket
The server is platform-independent and can run any program
Create a server program in C# and build to generate myProgram.exe,
1. using System;
2. using System.Threading;
4. //myProgram.cs
5. class Counter
6. {
7. static void Main()
8. {
9. for (int i = 1; i <= 10; i++)
10. {
11. Console.WriteLine(i);
12. Thread.Sleep(500);
13. }
14. }
15. }

You can copy myProgram.exe into c:\websocket for convenience
Open a command shell and goto c:\websocket and run below command
websocketd.exe -- port 80 myProgram.exe

It gave the above error because port 80 is already in use. We can validate by using netstat command.

So I will use port 8082 to run the WebSocket server.

websocketd.exe -- port 8082 myProgram.exe

WebSocket client object

With this API, you can send and receive messages to a server without having to poll the server.

Receiving messages

After the connection is established, we can receive messages using onmessage event.

var ws = new WebSocket('ws://localhost:8082/');
// this will establish connection with server at port 8082
//notice ws: this is new URL schema for WebSocket connection
ws.onmessage = function(event) {
console.log('Count is: ' + event.data);
}; // this will receive output from server in event.data

Sending messages

After the connection is established via onopen event, we can send messages using the send method.

ws.onopen = function () {
console.log('OnOpen');
ws.send('my message');
}

Log errors

Use onerror event to trap error generated from WebSocket,

ws.onerror = function (error) {
console.log('WebSocket Error ' + error);
};

ReadyState

If you remember, we have a ready state in XHR API. Similarly, WebSocket also maintains a connection state. It starts from 0 to 3,

0 | Connecting- the connection is not yet open
1 | Open- the connection is open & ready to communicate
2 | Closing- the connection is closing
3 | Closed- the connection is closed

Close

To close an open connection use close method, like ws.close();

Summary

The web is full of technologies and the intent is to make the web fast & better than before. Our quest shall be to give users good experiences and good performance applications. Please share your feedback/comments.

Voice of a Developer: Javascript WebSocket - Part 27

Introduction

WebSocket

Advantages of WebSocket