Monday, June 29, 2015

"Socket.IO Real-time Web Application Development" - book review

In this post I will share my thoughts on a book called "Socket.IO Real-time Web Application Development" written by Rohit Rai, published in 2013.
It has 6 chapters and 2 appendices in around 120 pages. This book is made for developers who want to start developing highly interactive and real-time web applications or multiplayer web based video games. The book starts with brief introduction to real-time server side of web applications. How it was and how it is now.
It then continues with building a simple chat application using NodeJS, ExpressJS, JQuery, Socket.IO and a templating engine called Jade. It is expected that the reader understands well JavaScript. Also NodeJS knowledge would be a plus but it is not necesarry as all needed aspects are well explained. 

Chapters:
  1. Going Real-Time on the Web. Covers history of XMLHTTPRequest, AJAX, FlashSocket, etc... and of course introduction to real-time web of today.
  2. Getting Started with Node.js. Covers brief introduction to Node.js programming. How to install it, how to import npm packages, and how to create a simple "hello world" application.
  3. Let's Chat. Explains how to start with Socket.IO on the server side but also on the client side. Some basic information what is what on the client/server and how it works.
  4.  Making it More Fun. This chapter is the longest one and I would recommend passing it in 2 or 3 parts with breaks between. It adds nicknames to chat users and "create rooms" functionality.
  5. The Socket.IO Protocol. Advantages od Socket.IO over WebSockets API. Socket.IO is much more capable and complex, therefore it needs dedicated protocol to function. It also covers all protocol types of messages that exist.
  6. Deploying and Scaling. Covers some information on how to keep your app on Node.js up and running and how to monitor background processes with Monit and Forever. Scaling with HAProxyNode Cluster and Redis.
  7. Appendix A: Socket.IO quick reference.
  8. Socket.IO Backends. Covers brief information about Socket.Io backends for Erlang, Google Go, Java, Perl and Python.
 The problems I faced while developing the sample chat application were:
  1. The book is made for Socket.IO version 0.9 which is discontinued and no longer available for download over npm. So I downloaded version 1.3.5.
  2. The protocol API is a bit different from version 0.9 to 1.3.5 so if you get deep into Socket.IO structure you'll be a bit confused.
  3. The web documentation is kind of poor so you will need to search the web for information how to get valuable data from the Socket.IO Server object.
My thoughts on the book, it is well made for what it was meant for, but the problem with these JS libraries is that they change very fast, so this book is getting old already. On the other hand it gives a good example to practice with newer versions of Socket.IO so therefore I recommend it for new Socket.IO developers.
There were some inconsistencies but all in all it serves its function. I give 4.2/5.

I uploaded the demo chat application on this location:
Its not finished, because I have other things to do at the moment, but it is good start. I used https://www.openshift.com/ with Node.js 0.10 with preinstalled HAProxy load balancer. 
If it is unavailable the service sets the app to idle state. So remind me or write an email if it stopped, to restart it.

Notes:
  •  Socket.IO creates a room for each tab you have on every browser. So if you have two tabs on Chrome and three tabs in Firefox connected to Socket.IO server, there will be 5 rooms generated for you inside the server state. 
  •  Socket.IO creates unique id for each socket connected to the server and that same id will be for a pregenerated room for the socket. You can create your room with custom name, and the socket you are using will be in two rooms, yours and the pregenerated one.
  •  Be careful how you connect to namespaces because the internal server state might get mess and you cannot get information properly. 
  • Socket.IO is easy to code. The API is same on both server and client.It works siemlesly though it is over HTTP layer.
Useful links I found on the web about Socket.IO:

https://github.com/SocketCluster/socketcluster
https://en.wikipedia.org/wiki/WebSocket
https://forums.openshift.com/keep-getting-program-node-serverjs-exited-with-code-8-and-503-service-unavailable
http://psitsmike.com/2011/10/node-js-and-socket-io-multiroom-chat-tutorial/
https://www.npmjs.com/package/roomdata
http://fzysqr.com/2011/02/28/nodechat-js-using-node-js-backbone-js-socket-io-and-redis-to-make-a-real-time-chat-app/
http://howtonode.org/websockets-socketio
http://coenraets.org/blog/2012/10/real-time-web-analytics-with-node-js-and-socket-io/
http://ejosh.co/de/2015/01/node-js-socket-io-and-redis-intermediate-tutorial-server-side/
https://en.wikipedia.org/wiki/Appserver.io

Thursday, February 26, 2015

How to structure you JS application

According to my reasearch which I was doing in past few months I got to some conclusions on how to structure your application for best code reusability.

Several patterns come to my mind, Module, Namespace, immediate functions, returning objects, using subobjects, using capitalized letters for functions/variables as "Constants", function scope and making accessor methods, JS constructors, using Yuidoc and Jasmine for better code quality.

Download the code from here: https://github.com/bluePlayer/practices/tree/master/AppStructure

Here is roughly what I am thinking about:

var externalJSLibrary = {},
    jquery = {},
    extJS = {},
    expressJS;

window.APP = window.APP || (function (wdo, lib1, lib2, lib3) {'use strict';
    var version = "1.0.0",
        config = {},
        parent = null,
        jqueryObj = lib1,
        extJSObj = lib2,
        expressJsObj = lib3,
        windowDocumentObject = wdo,
        MY_APP_NAME = "MyJSApplication",
        MY_EXCEPTION_MESSAGE = "My exception message",
        MY_APP_CONSTANT = "some message";

    return {
        Exceptions: {
            MyFirstException: function () {
                return {
                    message: MY_EXCEPTION_MESSAGE,
                    name: "MyFirstException"
                };
            }
        },

        Constants: {
            MY_APP_NAME: function () {
                return MY_APP_NAME;
            },
            MY_APP_CONSTANT: function () {
                return MY_APP_CONSTANT;
            }
        },

        Events: {
             keyDownEvent: function (event) {
                 // do some stuff when some key is pressed down on 'keydown' event.
             },

             keyUpEvent: function (event) {
                 // do some stuff when some key is released on 'keyup' event
             },

             keyPressEvent: function (event) {
                 // do some stuff when 'keypress' event was detected
             }
        },

        initApp: function (someObject, config) {
            var i;

            for (i in someObject) {
                if (someObject[i] !== null && typeof someObject[i] === 'object') {
                    if (someObject[i].hasOwnProperty('init')) {
                        someObject[i].init(config);
                    }
                    parent.initApp(someObject[i], config);
                }
            }
        },

        namespace: function (nsString, newObjectDefinition) {
            var parts = nsString.split('.'),
                helperObject = {},
                that = this,
                i = 0,
                field = {};

            if (parts[0] === that.Constants.MY_APP_NAME()) {
                parts = parts.slice(1);
            }

            for (i = 0; i < parts.length; i += 1) {
                if (that[parts[i]] === undefined) {
                    for (field in newObjectDefinition) {
                        if (newObjectDefinition.hasOwnProperty(field)) {
                            helperObject[field] = newObjectDefinition[field];
                        }
                    }
                    that[parts[i]] = helperObject;
                }
                that = that[parts[i]];
            }
            return that;
        },

        customFunction: function (a, b) {
            if (b < 0) {
                throw new parent.Exceptions.MyFirstException();
            } else {
                return 0;// do some stuff with a and b
            }
        },

        doSomeStuffWithJquery: function (someUrl) {
            jqueryObj.ajax({
                url: someUrl,
                xhrFields: {
                    withCredentials: true
                }
            });
        },

        doSomeStuffWithExtJS: function () {
            extJSObj.drawGraph();
        },

        doSomeStuffWithExpressJS: function () {
            expressJsObj.connectWithNodeJS();
        },

        init: function (configObject) {
            config = configObject;
            parent = this;
            parent.initApp(parent, config);
        }
    };
    }(window.document, jquery, extJS, expressJS));

window.APP.namespace('MySubObject', (function (lib) {'use strict';
    var config = {},
        parent = null,
        someLibrary = lib,
        MY_CONSTANT = "my constant",
        MY_EXCEPTION = "my exception";

    return {

        Exceptions: {
            MyNewException: function () {
                return {
                    message: MY_EXCEPTION,
                    name: "MyNewException"
                };
            }
        },

        Constants: {
            MY_CONSTANT: function () {
                return MY_CONSTANT;
            }
        },

        name: "MySubObject",

        myCustomFunction: function () {
            // do some stuff
        },

        init: function (configObj) {
            config = configObj;
            parent = this;
        }
    };
    }(externalJSLibrary)));

window.document.addEventListener("DOMContentLoaded", function (event) {'use strict';

    var myApp = window.APP;

    myApp.init({
        "event": event,
        otherConfig: {}
    });

    window.document.addEventListener('keydown', myApp.Events.keyDownEvent);
    window.document.addEventListener('keyup', myApp.Events.keyUpEvent);
    window.document.addEventListener('keypress', myApp.Events.keyPressEvent);

    });

"JavaScript Patterns" - book review

Hello. In this post I will share my thoughts on a book called "JavaScript Patterns" written by Stoyan Stefanov. Published in 2010 this book in about 210 pages covers the most important patterns that you can use in JavaScript to ease you work with this language. My guess is that this book is not for beginner JavaScript programmer, but you can always read this great book by Douglas Crockford, "JavaScript: The Good Parts" as an intro to JavaScript. These two books go hand in hand. Check my other book review here: http://tunephp.blogspot.com/2014/11/javascript-good-parts-book-review.html
If you really want to learn proper JS programming read both of them, first "JS the good parts" and then "JS Patterns" and try some programming practices in Firefox/Firebug.

The book has 8 chapters and has lot of useful code snippets you can use in building your brand new JavaScript application.

  1. Intruduction. Explains basic concepts of JS, like there are no classes in JS, everything is a object including, functions, arrays, objects etc... It also notes that you can use strict ("use strict", ECMAScript 5) mode, a modification of JS that removes some of the bad parts in JS. This chapter also introduces JSLint and the Console as debugging tools. You should always check your code with JSLint.
  2. Essentials. This chapter covers one of the main drawbacks in JS, and those are global variables. It also gives some tips how to avoid using too many globals, how to use "for", "for in" loops, avoiding implied typecasting with "==" sign, number conversions with parseInt() and parseFloat(), writing proper code, indentation, writing comments and using Yuidoc and JSLint.
  3. Literals and Contructors. It covers Object literal ({}) notation, JS constructors and naming convention for them and how to avoid problems using constructors. Array literals, check for "Arrayness" (arrays are objects in JS), working with JSON, regular expressions, primitive wrappers and throwing Errors/Exceptions.
  4. Functions. Covers function decalrations vs function expressions. Variable hoisting, function scope, function callbacks, returning functions, self defining functions, immediate functions and couple of useful tricks like memoization, curry, init-time branching etc... Probably the most important chapter in the book, you must not miss it as functions are the hearth of JavaScript.
  5. Object Creaing Patterns. Some object creating patterns like namespace patters(there is a very useful function for creating a tree of subobject, you can use it in your project.), private members, how to achieve real privacy in JS, Module pattern, Sandbox patterns, static members, JS "Constants", Chaining pattern etc... This chapter gives you better idea how to structure your code so that your project doesn't have trouble in the end.
  6. Code Reuse Patterns. Classical vs Prototypal inheritance patterns. You should avoid Class inheritance in JS since it is just a "syntaxic sugar", and always use Prototypal inheritance. This chapter also mentions some useful code reuse techniques, like borrowing methods, copying properties, some Class patterns etc...
  7. Design Patterns. This chapter covers how to code basic software engineering patterns in JavaScript, probably a chapter you don't want to miss. Singleton, Factory, Iterator, Decorator, Strategy, Facade, Proxy, Mediator and Observer. 
  8. DOM and Browser Patters. Covers some tools/concepts/patterns that can be used in a browser, like how to manipulate DOM tree, event handling, long running scripts, Ajax alikes, JSNOP, combining JS scripts, minifying, Loading techniques and preloading.
 So yes, this book cover very useful features of JavaScript and how to use them in browser. If you really want to become a web dev. this is the right book for you.

There are similarities with "JavaScript: The Good Parts" in the beginning, I felt like I was reading Doug's book again, but that is ok. It has lot of code and it is well explained so my grade for it is 4.5/5. Defineitely a book you should read.

Monday, February 23, 2015

Introducing new project called ZadachiJS

In the past few weeks I have been working on a new project called ZadachiJS. It is adapted for Macedonian public and the docs are written in Macedonian using english letters. It is basically a web application that has no GUI and all output is sent to the console, ofcourse the output is in Macedonian. It contains programming practices which could be made in any programming language and it is based on a book called „Збирка Алгоритми и Програми“, од Ѓорги Јованчевски, Билјана Стојчевска и Невена Ацковска or in english, "Collection of Algorithms and Programs" written by Gyorgy Yovanchevsky, Bilyana Stoychevska and Nevena Atckovska. I couldn't find english version of it, but I could in Macedonian. Not sure if there is going to come an english version. So if you want to understand this project better learn Macedonian, because probably I won't find time to translate it in English, who knows.

Збирка Алгоритми и Програми
Збирка Алгоритми и Програми

The JavaScript part consists of one global object called Zadachi and all other stuff are inside of it.
You can browse the code here: https://github.com/bluePlayer/practices/tree/master/ZadachiJS
or check the demo here: http://jspractices-blueplayer.rhcloud.com/Zadachi and the docs here: http://jspractices-blueplayer.rhcloud.com/Zadachi/docs
Jasmine.js tests are here: http://jspractices-blueplayer.rhcloud.com/Zadachi/SpecRunner.html

Thursday, February 19, 2015

New location for JavaScript practices.

Check this link for my new page regarding JavaScript demos.

http://jspractices-blueplayer.rhcloud.com/

GitHub: https://github.com/bluePlayer/practices

Note: If some of the demos is unavailable write me on this post or an email, because openshift sets the process to idle state if the page is not accessed often.

Wednesday, January 28, 2015

JavaScript "constants"

I did a bit of research about constants in JavaScript. Well guess what, there are no constants in JavaScript. :)

So how do you implement "constants" with JavaScript patterns and syntax?

Note: The next text might require more readings but if will help you learn lot of JavaScript basics. Probably you will never have to use this code, since existing JS librarires have already solved this issue somehow.

Constants are important concept of every programming language and definetelly you should use them whenever possible. For example let just say you have an error message that needs to be printed in the output field from several places in your code. How are you sure that each time you write that string of message is written without missing letters? Sometimes you are tired, sometimes you rush and therefore errors are inevitable. So to prevent this you create a constant that contain that string and use the constant instead of writing the string.

Example constant: CANNOT_DIVIDE_BY_ZERO = "Cannot divide by zero!";

I have been developing a practice application which you can access live here: http://jspractices-blueplayer.rhcloud.com/Calculator/ and the docs are here: http://jspractices-blueplayer.rhcloud.com/Calculator/docs
Also you may preview the HTML/JavaScript code here: https://github.com/bluePlayer/practices/tree/master/CalculatorJS.
The code also passes JSLint test, with only "jslint browser: true" option.

There are two important functions which you should check, Constants() and namespace().
Constants() is a constructor function and namespace() creates subobject of the main application object called window.APP.
Lets start with namespace() function. It recieves two parameters, first the name of the subobject that will be created and second is the configuration object which contains necessary properties and methods that will be contained in this new subobject. namespace() creates new subobject Constants using the new keyword, secondly creates constMap subobject which will contain accessible keys for each of the constants.

Example:

window.APP.namespace('Trigonometry', (function () {
    return {
        PI: 3.14,
        doSomeStuff: function () {

        }
    }
}()));

This example creates Trigonometry subobject of window.APP and Trigonometry contains two subobjects, Constants with methods, get(), set(), isDefined() and list() and constMap which has one key/value, PI: "PI" and ofcourse the function doSomeStuff() which does nothing.

So with my solution you can create immutable constants by just passing key/value pair (key must be all capitalized letters) and the code will create it for you. Well if we create a PI constant how do we get the value? The solution is straight forward but it looks very ugly and big.

Example:

console.log(window.APP.Trigonometry.Constants.get(window.APP.Trigonometry.constMap.PI));
// prints 3.14

Alternatively you can pass the name of the constant if you know it:

console.log(window.APP.Trigonometry.Constants.get("PI"));

hahah :D

To improve this solution a bit I created an application wide function in APP namespace called getConst(). You send the path of the constant in string format.

Example:  

console.log(window.APP.getConst('APP.Trigonometry.PI')); // prints 3.14

What happens in this function is parsing the string parameter and getting to the constant value trough the application tree. But this solution is against the "Constants" concept. Either I should be careful to write that string parameter properly or I should create a variable/property inside APP to contain that string and then use it in the above example, like so:

window.APP = window.APP || (function () {
    var TRIGONOMETRY_PI =  'APP.Trigonometry.PI';
    return { 
        getConst: function (constantPath) {
            // code
        },
        doSomeStuff: function () {
               console.log(this.getConst(TRIGONOMETRY_PI)); 
        }
    }
}()));

window.APP.doSomeStuff(); // prints 3.14


So this brings us to the best solution to the problem, and that is creating variables with capitalized letters in closure and then using capitalized accessor methods for them.

Example: I will create GRAVITY = 9.8 constant in new subobject of APP, called Physics.
window.APP.namespace('Physics', (function () {
    var GRAVITY = 9.8;
    return {
          GRAVITY: function () {
               return GRAVITY;
         }
    };
}()));

console.log(window.APP.Physics.GRAVITY()); // prints 9.8

This will create subobject Physics in window.APP and it will contain constMap object with one key/value pair, GRAVITY which is function(). I changed namespace() function to create function in constMap if the capitalized key contains value of a function instead of a value.  If I just send this key/value pair: GRAVITY: 9.8, the namespace() function would have created key/value pair in constMap, like so: GRAVITY: "GRAVITY" and you have to access constant's value using the long statement in the previous examples.

To clear things up, you don't even need to create Constants() constructor in your application, you can use variable with closure and accessor methods with capitalized names to represent constants. I created this constMap subobject just to separate constants from other properties/methods in a given object. You don't even need it.

Note: there are some rummors that ECMAScript 7 or was it 6, will contain const keyword. Until then you can use capitalized variable and methods with closure to represent "constants".

If you have any thoughts on the topic, let me know.