Building a Captcha using HTML5 Canvas

CAPTCHA (/kæp.ə/, an acronym for “Completely Automated Public Turing test to tell Computers and Humans Apart”) is a type of challenge–response test used in computing to determine whether or not the user is human.[1]
The term was coined in 2003 by Luis von AhnManuel Blum, Nicholas J. Hopper, and John Langford.[2] The most common type of CAPTCHA was first invented in 1997 by two groups working in parallel: (1) Mark D. Lillibridge, Martin AbadiKrishna Bharat, and Andrei Z. Broder; and (2) Eran Reshef, Gili Raanan and Eilon Solan.[3] This form of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a CAPTCHA is sometimes described as a reverse Turing test.

This user identification procedure has received many criticisms, especially from disabled people, but also from other people who feel that their everyday work is slowed down by distorted words that are difficult to read. It takes the average person approximately 10 seconds to solve a typical CAPTCHA.[4]


On the similar lines, we are going to build a simple Captcha, which is going to validate a form before submitting it. Here is how it is going to look like

Live demo of the same can be found here:

So, let’s get started.


The Captcha module that we are going to create in this post can be tightly coupled with an existing form or can be used in a generic way.

We are going to have a container that the app owner is going to provide. The captcha and the input field are going to be created inside this container.

To generate the passcode, we are going to use  Math.random() in combination with a computed scenario of uppercase or lowercase letters.

The input field will be publishing two events on keyup.  captcha.success when the validation of text box value matches the generated passcode &  captcha.failed when the values do not match. The “form owner” is going to listen to these events and work with it to get to know if the captcha is valid or invalid.

In the sample form we are building, we are going to enable or disable the submit button based on the above events.

And we are going to style the text in canvas as well to add some randomness.

So, let’s get started.

Setup Simple Login Form

We are first going to setup a simple login form using Twitter Bootstrap 4. We are going to use Signin Template for Bootstrap for the same.

Anywhere on your machine, create a folder named  login-form-with-captcha and inside that create a new file named  index.html.

Update  index.html  as shown below

I have borrowed the structure and styles from Signin Template for Bootstrap and built the above page.

As you can see, the Sign in button is disabled on load. We will enable the button once the Captcha is valid. We will do this in the later sections.

If you open the page in the browser, it should look something like

A simple form for a simple job!

Setup Captcha

Now, we are going to setup the container where the Captcha is going to appear. Just above the button tag,  we will add the Captcha container

Next, we are going to create a file named  captcha.js in the  login-form-with-captcha folder and then we will link the same to  index.html  just after the form tag as shown below

The basic  captcha.js would be structured this way

The above code is an IIFE with a Module pattern.

If we save the above file and refresh the browser, we should see the following in the console

Now, we will flesh out the remaining code.

Develop Captcha module

Now that we have a basic structure, we will continue building the plugin. First we are going to setup the  init()


In  init(), we are going to do the following

  1. Get the captcha container
  2. If container does not exists, exit the initialisation
  3. Create a canvas element & an input text element
  4. Setup Canvas
  5. Setup Textbox
  6. Bind events on Textbox
  7. Generate Passcode
  8. Set Passcode
  9. Render component on page

The Updated  init() would look like


We are going to setup a canvas element as shown below

We are setting up a canvas with the width of the parent container and height of 75px.


The text box will be setup as shown below

We have updated the type of input field and added a className and a placeholder. Next, we are going to bind events to the input field. The .are the events that the parent application consuming this captcha would be listening to.


On keyup, we are going to validate the passcode against the input field

We have created 2 events

  1. When the validation is successful
  2. When the validation failed

Pretty straight forward.


Below is the logic to generate a random passcode.

Scripting to the rescue!


To  setPasscode() , we are going to add two more helper functions that create a random font color for a character.

And then finally


Now that we have all the pieces ready, we will render the canvas and text box on the page

This concludes our Captcha module.

The final  catpcha.js would be as follows

Setup Validation

Now, we are going to setup the validation on the form. After including  catpcha.js in the  index.html

The complete  index.html would be as follows

Save all the files and when we refresh the page in the browser, we should see

You can find the above code here: arvindr21/captcha.

Thanks for reading! Do comment.

Build & Publish a Node Package Module (NPM)

In this post, we are going to build and publish a Node Package Module (NPM). The module we are going to build is a simple utility which will take a  Web supported color name as an argument and spits out the HEX & RGB values for the same. We are going to use a Test Driven Development (TDD) style of coding for building this module.

I have taken the color names from – Thanks to them!

Before we get started, here is a quick preview of the CLI version in action

The story behind rebeccapurple. RIP Rebecca Meyer.

Getting Started

Below are the steps we are going to follow

  1. Setup Yeoman
  2. Install Generator
  3. TDD Colorcode
  4. Validate Code Coverage
  5. Push to Github
  6. Setup Travis CI
  7. Setup Coverall
  8. Publish to NPM

Setup Yeoman

If you are new to Yeoman, Yeoman is

What is Yeoman?

Ripping off from

Yeoman helps you to kickstart new projects, prescribing best practices and tools to help you stay productive.

To do so, we provide a generator ecosystem. A generator is basically a plugin that can be run with the yo command to scaffold complete projects or useful parts.

Through our official Generators, we promote the “Yeoman workflow”. This workflow is a robust and opinionated client-side stack, comprising tools and frameworks that can help developers quickly build beautiful web applications. We take care of providing everything needed to get started without any of the normal headaches associated with a manual setup.

With a modular architecture that can scale out of the box, we leverage the success and lessons learned from several open-source communities to ensure the stack developers use is as intelligent as possible.

As firm believers in good documentation and well thought out build processes, Yeoman includes support for linting, testing, minification and much more, so developers can focus on solutions rather than worrying about the little things.

So ya, Yeoman is like your File > New > NPM project | fill the project information and boom! A NPM project gets generated; but from command line.

To install Yeoman globally, run

And to validate, run

Install Node.js

Before we go further, make sure you have Node.js installed on your machine. You can follow this post Hello Node for same. I am using the following versions


In this post, we are going to use a Yeoman generator named generator-np to scaffold our base for building the NPM. To install the generator globally, run

Once the installation is done, we are good to scaffold our app

Scaffold color2code

Anywhere on your machine, create a folder named color2code  and open a new terminal/prompt there. Now, run

And you can answer the questions as shown below

This will take a moment to complete scaffolding.

Once the project scaffolded, we should see something like

In this project, we are going to follow a Test Driven Development approach. We will first update the  test/index.js  file with all possible scenarios and then get started with the code.

Next, we are going to work in src  folder to update the cli.js  and the  lib/index.js  files.

Before we get started, let’s quickly look at the solution.

Color2Code Solution

The app we are going to build is a simple utility that takes a popular web supported color names and spits out the RGB and HEX values of the same.

We are going to maintain a collection of all the web supported colors and their HEX values. And in our code, we are going to read color name and fetch the HEX value. We then use the HEX value to generate the RGB version of the same.

Sounds simple right?

So, let’s see how to work with this solution & build a NPM.

Update project configuration

I have made a few changes to the project so that things are a bit more easy to manage.

Open  .eslintrc  and make the changes to the properties shown below

Next, we are going to update  package.json  as highlighted below

Finally, update  .travis.yml as shown below

That is all!

Test Driven Development – TDD

To work with the code base we have just scaffolded, we are going to use TDD or Test Driven Development. We are going to write the test cases first and then develop our code.

TDD is not for the weak hearted. Seeing your application fail even before writing a single line of code takes courage.

You can read more about TDD here: Test Driven Development by Example

Write Test Cases

To get started, we are going to write the test cases first and see our app fail and then start making the required changes to our code to fix it.

Open  test/index.js and update it as shown below

The above file outlines 5 scenarios

  1. If there is no color name provided to our NPM
  2. If one color name is provided to our NPM
  3. If more than one color names are provided to our NPM
  4. If an invalid color name is provided to our NPM
  5. If an invalid color name is provided along with valid color names to our NPM

The code we are writing should satisfy the above 5 scenarios.

Now, let’s run the NPM and see it fail.

Run the NPM

We are going to use nodemon to watch our app for changes and rebuild our application.

To install nodemon, run

Once nodemon is installed, from inside color2code  folder, run

If the command ran successfully, we should see an error blob stating that tests have failed.

Yay! we did it.

Now, let’s get cracking on fixing these cases.

PS: Keep the nodemon running in the terminal/prompt. As we keep making changes and saving files, the tests will be executed again.

Develop the NPM

First, we are going to get a dump of Web colors. Thanks to, we have list of 148 color names.

Create a file named  colors.json inside  src/lib folder and update it as shown below

Save the file and you should see that nodemon  has detected changes to the src  folder and is running the prepare  task again. The tests are still failing.

Next, inside  src/lib folder, create a file named  utils.js and update it as shown below

On Line 1, we have required the colors hash.  hexToRGB() takes a HEX code and returns the RGB hash for the same.  processColor() takes in the color name and returns the final result.

Save the file and still the tests do not pass.

Awesome! let’s continue

Update  src/lib/index.js as shown below

Here we are processing the options and responding accordingly.

Save the file and Boom!

All the tests pass! And our NPM works!

Now, we will udpate  src/cli.js as follows

This concludes our development.

Simulate NPM install & Test

If you would like to simulate an NPM global install and test your app before publishing, you can do so by running the below command from inside the  color2code folder

And we should see something like

And from anywhere on your machine you can run

Awesome right!

Code Coverage

We have written code and we have written test cases. Now, let’s take a look at the code coverage.

From inside  color2code folder, run

And we should see something like

You can also open  coverage/index.html to view the report in the browser. It should look something like this

So we are good to move our code to Github.

Push color2code to Github

You can push your fresh NPM to git to maintain it and let other people look-see/contribute to your code. For that we will follow the below steps

  1. Create a new Github repo:
  2. Run the following commands

PS: Update your repo URL as applicable

Voila! The code is deployed to Github. You can checkout my code here: arvindr21/color2code

Now that this is done, let’s setup Travis CI and Coveralls.

Setup Travis CI

Now that the repo is setup in Github, we will have a CI system in place. A Continuous Integration System keeps a tab on your repo for new changes and runs test cases on new changes and let’s you know if anything is broken.

Travis CI is a popular open source solution. You can read more about Travis CI here. We are going to use the same for managing our NPM.

If you open your Github repo, at the top of your readme, you should find a section as below

Click on “build | unknown” and you should be taken to Travis CI. In Travis CI, you should see a page like below

Activate repository.

From next time onwards when ever there is a push to the repo, the CI will kick in and check if the build has passed.

Before we trigger a build, we will setup Coveralls.

Setup coveralls

Quoting from

Coveralls takes the build data from whichever CI service your project uses, parses it, and provides constant updates and statistics on your projects’ code coverage to show you how coverage has changed with the new build, and what isn’t covered by tests. Coveralls even breaks down the test coverage on a file by file basis. You can see the relevant coverage, covered and missed lines, and the hits per line for each file, as well as quickly browse through individuals files that have changed in a new commit, and see exactly what changed in the build coverage.

Back to our repo and at the top of readme, click on “coverage | unknown” and you should be redirected to Sign in and Click on the “+” sign in the menu on left hand side and search your repo here. Once you find it, enable coveralls for this repo.

And that is all, we are done.

Trigger Build

Now, let’s go back to Travis and trigger build from “More options” menu on the right hand side. And you should be shown a popup, fill it as applicable – trigger custom build

And once the build is completed, you should see something like this

Sweet right! Our NPM works from versions 4 to 10. Yay!!

This trigger will happen automagically when ever there is a new commit/Pull request.

The final step if build passes is to update coveralls. If we navigate to coveralls for our repo, we should see something like

Travis arvindr21/color2code

We have a code coverage of 90%, which is good, considering we have only written few lines code.

We can also find out which files has what amount of coverage, as shown below

You can drill down further to analyse the issues.

With this we are done with our CI and Code coverage setup. If we go back to our Repo’s readme file, we should now see

Now, we are going to publish the color2code to

Publish color2code to NPM

To push color2code to NPM, we need to have an account with Once you have signed up and activated your account, you can login to the same from your command prompt/terminal.


Once logged in, make sure you are at the root of  color2code folder and run

And boom your color2code  NPM is published.

If you get an error, which mostly will happen because you have used the same name as mine – color2code. You need to use another name for your module in package.json  file and then try publishing.

Your NPM is published. Navigate to to see the module we have just built.

With this our repo badges would look like

Hope you have learned how to build, publish and manage your own NPM!

Thanks for reading! Do comment.

Deploying a Node.js Docker container to Heroku

In the last post titled Developing Node.js applications in Docker, we have seen how we can work with Docker as our development environment.

In this post, we are going to take the app that we have built named docker-node-app and deploy it to Heroku as a Docker container.

The sample code used in this post can be found here: docker-node-app.

So, let’s get started.

Setup Heroku

The first thing we need to do is download and install Heroku tool belt on our local machine.

Download Toolbelt

You can follow the instructions given here: Install Heroku Toolbelt to install Heroku tool belt for your Operating System.

Setup Account

If you do not have a Heroku account, you can signup here.


Now that we have Heroku installed, we will login. Open a new command prompt/terminal and run

Next, we need to login to the container registry. Run

Once we have successfully logged in to Heroku & Heroku container registry, let’s work with Docker.

Setup Docker

The first thing we are going to do is download Docker for our Operating System.


To Install Docker on our machine, navigate to here & download the software for your OS.

Test Download

Once Installed, you can open up a command prompt/terminal and run  docker ps and you should see something like

At this point, we have both Docker as well as Heroku installed on our machine.

Next, we are going to containerize our app and deploy it to Heroku.

Setup docker-node-app

If you have not already done, please go through Developing Node.js applications in Docker, where we see how to develop Node.js applications using Docker. We are going to begin at the ending of that post.

Clone docker-node-app

Now, we are going to clone docker-node-app from From anywhere on your machine, run

And then  cd docker-node-app .

Fix Port

We need to make a change to the Dockerfile  to fix the port. While deploying to Heroku, port would be assigned by Heroku.

Open Dockerfile  and update it as shown below

That is it, we are all set to deploy our awesome container app to Heroku.

Deploy to Heroku

Now, we are going to deploy to Heroku. We are going to follow the below steps

  1. Heroku create new app (one time)
  2. Heroku container push – Create and push the container to Heroku Container Registry
  3. Heroku container release – Release/run the container app
  4. Heroku open – Launch the app

From inside  docker-node-app run

This will create a new Heroku app.

Next, we will push the container

Now, we will run the container

And finally open the deployed app run

And we should see

Voila! Our Node.js that we have containerized while development is now deployed to Heroku with ease.

Development & Deployment simplified!

PS: I am shutting down the above Heroku app, as it does not have any thing specific to showcase.

Hope you got an idea as to how we can deploy Node.js containerized application to Heroku.

Thanks for reading! Do comment.

Developing Node.js applications in Docker

In this post, we are going to look at developing a Node.js application using Docker as the development environment.

Why Dockerize my development?

You may ask, what is wrong with my current setup? Why should I “Dockerize my Node app”?

Well for starters, your development environment need not be the machine on which you are coding.

Let’s say that you are new to a project and you are getting started with your environment setup and you are installing an awesome plugin like grunt-contrib-imagemin and you find that its dependency libpng is missing on your machine. You Google and try to solve the problem yourself because a. you are the new member in the team and you want to prove yourself and b. you don’t know anyone in the team yet.

Everything is good so far, you were able to fix the libpng issue and now you run npm install  again and you notice that grunt-yellowlabtools needs phantomjs and for some reason the download fails while installation. Again for the above said reasons, you are too shy to approach someone so you spend the first day on the project installing the dependencies and finally setting up your environment and running your project successfully.

Very productive day one.

Now, imagine, one your first day, all you would need to do is

  1. Install Docker
  2. Run docker run -it -p 3000:3000 myproject/my-app:0.1.0

And voila, the app is running on your machine. And you are all set to get started. How about that?

4 reasons why?

Here are a few reasons why you need a “Dockerized” development environment:

  1. Your production environment will almost always never be same as your development environment. So you can directly work on your production environment setup on your local to avoid “surprising” deployment issues.
  2. Easy for your devops team to work and scale with containers in higher environments than your local
  3. One developer machine can run multiple (Node.js) applications in an isolated way
  4. Docker compose lets us run dependent pieces of softwarer in an micro service architecture easily

Now that you feel it is a good idea to Dockerize your development environment, lets look at how.

How to Dockerize a Node.js app?

We are going to follow below steps

  1. Setup Docker
  2. Build a simple Node.js application
  3. Build a Docker image
  4. Create a container from the Image and start developing.

Before we actually get started, let’s look at what is Docker.

What is Docker?

Docker is a computer program that performs operating-system-level virtualization also known as containerization.

To understand the above jibber-jabber, take a look at this video

Quite a simple and powerful concept.

If you would like to dig deeper in the world of containers, checkout this playlist from Vmware

Now that we understand the why, what and how; let’s get our hands dirty by building a Dockerized Node.js app.

Getting Started

First we are going to install Docker

Install Docker

For this tutorial, we are going to use Docker Community Edition (CE). To Install Docker on our machine, navigate to here & download the software for your OS.

Once Installed, you can open up a command prompt/terminal and run  docker ps and you should see something like

The above output shows that there are no images running.

Now, lets quickly test drive Docker.

Run  docker run busybox echo "hello from busybox"  and you should see that the busybox image downloaded locally and run the echo command that we have provided. The output would be as follows.

Now that we got the Docker installation done & verified, let’s move on.

Build a Node.js App

Now, we will setup a simple Node.js app. If you are planning to run this application on your local machine, make sure Node.js is setup on your machine. You can follow this post Hello Node. I am using the following versions

If you are going to run the app directly in a docker container, you can skip local installation of Node.js.

Anywhere on your machine, create a folder named  docker-node-app and open a new terminal/prompt there.

First, we are going to initialise a new Node.js project. Run

This will create a package.json  with default contents. Update it as shown below, as applicable

Do note that I have added a script named  start, which launches the app that we are going to create in a moment.

Now, we are going to build a simple app, which prints the environment variables on the machine it is running.

Inside docker-node-app folder, create a file named index.js  and update it as shown below

All we are doing is iterating the  process.env object & building a string with the key and value.

Test drive the Node.js application

Let’s test the application we have built. You can do this only if you have Node.js installed on your machine.

You can simply run


If you do not have nodemon on your machine, you can install it as follows

Once the server is up and running, navigate to http://localhost:3000/, we should see

Isni’t very brave of me to publish my machine’s environment variables out in public :/ 

Now that we have validated that the app is working fine, lets “containerize” it.

Build a Docker image

Now that we have our sample app running, let’s create an image. Inside docker-node-app  folder, create a file named Dockerfile and update it as shown below

On line 2 : we set the base image in which our app is going to run. Which is a Node image with version 8 installed.

On line 8: we create a directory where our source code would reside in the container

On line 11: we switch to the working directory

On line 15: we copy our current source code to the image

On line 18: we install nodemon globally.

On line 21: we install any other dependencies defined in  package.json

On line 24: we expose port 3000 so the host machine can access the app

On line 27: we start the Node.js app on boot of the container

Simple right?

Now to make sure we copy only what we need, we will create a file named  .dockerignore at the root of  docker-node-app and update it as shown below

Now that we are done with setup, we will build the docker image. From inside   docker-node-app  folder, run

docker-node-app docker build -t arvindr21/docker-node-app:0.1.0 .

Do note that  arvindr21 from the above command is my Dockerhub username. If you are planning to push this image to Dockerhub, it needs to be with your Dockerhub username.

Once the build kicks off, you should see logs as shown below

Now, if we run  docker-node-app docker images we should see

Awesome! Now our image is ready. We need to create a container from this image and voila our app  will be running from inside an image.

Create a conatiner & Run the app

This is the most important step in this process.

To run our Node.js app in a container, we are going to

  1. Download the code base on our local machine
  2. Point the volume of the container to the folder where the code is downloaded and run the image
  3. Open the local copy of code on your host machine text editor
  4. Start making changes

So, let’s move on. Since the codebase is already on our machine, we are not going to download it. If you project files are hosted on a remote server, download them to your local.

Next, we are going to create a container from the image and point the volume to docker-node-app  folder, as shown below

docker-node-app docker run -it -p 3000:3000 -v ${PWD}:/usr/src/app arvindr21/docker-node-app:0.1.0

/usr/src/app  : is the folder in the container

${PWD}  : is the folder on the host machine where the code is present. I am running the above command from the same folder, hence I am passing in the present working directory variable

3000 : is the port mapping between host machine and container.

Note: If you want to run this app as a background process pass a  -d or a deamon flag as shown below

docker-node-app docker run -itd -p 3000:3000 -v ${PWD}:/usr/src/app arvindr21/docker-node-app:0.1.0

If everything goes well, we should see

Now, navigate to http://localhost:3000/ and we should see something like

Do notice that the values now have updated to the environment variables from the container. Do notice the  HOSTNAME property, it is displaying a value of  cb0852847690. Now, from the host machine, run  docker ps and we should see something like

Do not the  HOSTNAME matches the  CONTAINER ID.

So, ya, it works.

Now to the awesome part, live reloading.

Live reload the container app

Now, we have our app running in a container and the code base on our host machine, let’s add a change to the code base on our local machine and see the changes reflect in the container app.

Open  index.js and update it as shown below

I have added a new piece of code to display the time.

Save the file on your host machine and we should see the following in the terminal/prompt

Now, back to http://localhost:3000/ and we should see

Voila! The time appear-th! Keep refreshing to see the value change.

Now, when you are done with the development, you can push the code to the remote repository and shutdown your Docker image. And once when you are ready to code, you can bring up the Docker image.

Adding code files

Okay, so we are able to make changes to an existing file, what about adding a new file. Let’s try that out.

Inside  docker-node-app folder, create a file called as  date.js and update it as shown below

All we have done is externalized the logic to get current date. Now, open  index.js and update it as shown below

And you should see a message in the prompt/terminal that the server restarted due to changes. Now if we go back to browser and refresh, we should see that the output does not change but we are loading the date from an external file.

Simple and powerful development environment that is development and deployment friendly.

You can find the code used in this post here: arvindr21/docker-node-app

Thanks for reading! Do comment.

Learning Ionic

For the past 3 months, I was involved in a writing an awesome book on Ionic, thanks to Packt Publishing.


This book is part of a learning series, where the main goal of the book was to introduce developers to Ionic and get them acquainted with it. This books consist of 9 chapters and an appendix. They are as below

Ch. 1 Ionic – Powered by Angularjs Reintroduces AngularJS from Ionic perspective.
Ch. 2 Welcome to Ionic Introduces Mobile Hybrid architecture, Cordova and Ionic.
Ch. 3 Ionic CSS Components & Navigation Introduces CSS only components of Ionic. Examples on how to integrate these components with AngularJS.
Ch. 4 Ionic & SCSS Theming Ionic apps isn't a rocket science anymore.
Ch. 5  Ionic Directives & Services A deep dive into various Ionic directives and services, what they are how to use them.
Ch. 6  Building a Book Store App A hands-on example on building an Ionic app that integrates a REST API (with JWT support).
Ch. 7  Cordova & ngCordova Add Cordova support to your projects & learn how to work with ngCordova.
Ch. 8  Building a Messaging App Build a chat application using Firebase, Ionic and ngCordova. Share texts, Images & Geo location between friends.
Ch. 9  Releasing the Ionic Application Learn all the essentials needed to release the chapter to the app store.
Appendix Additional topics & tips I have added a few cool things that every Ionic developer must be aware of.

I have a created a GitHub Organization for Learning Ionic – here. This Organization consists of all the code examples explained in the book. All the examples are based on Cordova 5.0.0, Ionic CLI 1.5.0 & Ionic 1.0.0. I will try my best to keep these updated, as Ionic changes.

Big credit goes to Hemal Desai for finding me & getting me on board. Merwyn D’Souza – The super awesome content editor, who got approvals for this book to go till 388 pages from the initially agreed upon 250 pages, just to make sure the readers get the best content. #respect. Also the only one person who went through the entire book like 4 times reading my crappy English. #sorryforthat. The book is what it is because of your efforts! #thanks.

Another awesome person I got to work with is Shashank Desai – The technical editor. I was honoured to work with a person with such high credentials & very happy that he will be moving to the Project manager role after this book. Wishing him loads of luck.

And a very special “Thank you” to the entire team Packt Publishing team involved in getting 388 pages book out in less than 3 months. Kudos!!

The reviewers

  • Bramus Van Damme
  • Ian Pridham
  • Indermohan Singh

who were very very insightful in finding gaps in the content & the code examples. They improved the quality of a book to what it is now. It was an amazing experience working with you guys.

Finally, a very special Thanks to Mike Hartington (Ionic core team member) for the Forward. This definitely added a lot of value to the book.

And the best part now, where can you buy this book from

  1. Packt Publishing
  2. Amazon – Paper Back
  3. Amazon – Kindle

Do let me know what you guys think.

PS: A big sorry to all the people who tried to reach me on my blog or personally in the last three months. I was super busy in getting this book out. Hope I am not too late to answer your questions now.

Thanks for reading! Do comment.

Electron, WordPress & Angular Material – An Offline Viewer

Imagine that you are at the airport, waiting for your flight and you hear a couple of guys sitting behind talking about Nodejs, Angularjs, MongoDB and you being a full stack developer and blogger start eves dropping. And all of sudden one guy mentions.. “Dude, you should totally check out this awesome blog.. It is titled ‘The Jackal of Javascript’ & that guy writes sweet stuff about node webkit, ionic framework and full stack application development with Javascript”. And the other guy says “cool..” And with his airport wifi connection starts browsing the blog on his laptop.. With in a few moments he loses interest because the pages aren’t loading.

What if the owner of the wordpress blog had an offline viewer and the first guy showed all the awesome stuff in the blog to the other guy on his laptop without any internet connection, wouldn’t that be cool?

So that is what we are going to do in this post. Build an offline viewer for a wordpress blog.

Below is a quick video introduction to the application we are going to build. 


Sweet right? 

So, let us stop imagining and let us build the offline viewer.

You can find the completed code here.


As mentioned in the video, this is a POC for creating an offline viewer for a wordpress blog. We are using Electron (a.k.a Atom shell) to build the offline viewer. We will be using Angularjs in the form of Angular Material project to build the user interface for the application.


As shown above, We will be using the request node module to make HTTP request to the wordpress API to download the blog posts in JSON format and persist it locally using DiskDB.

Once all the posts are downloaded, we will sandbox the content. The word sandbox here refers to containment of user interaction & experience inside the viewer. As in how we are capturing the content and replaying it back to the user. In our case, we are sandboxing the images and links, to control the user experience when the user is online or offline. This is better illustrated in the video above.

The JSON response from the WordPress API would look like :

If you replace my blog domain name from the above URL with your WordPress blog, you should see the posts from your blog. We will be working with content property of the post object.

Note : We will be using recursions at a lot of places to process collections, asynchronously. I am still not sure if this is an ideal design pattern for an application like this.


The offline viewer is a bit complicated in terms of number of components used. Before you proceed, I recommend taking a look at the following posts

Getting started

We will be using a yeoman generator named generator-electron to scaffold our base project, and then we will add the remaining components as we go along.

Create a new folder named offline_viewer and open terminal/prompt there.

To setup the generator, run the following

npm install yo grunt-cli bower generator-electron

This may take a few minutes to download all the once modules. Once this is done, we will scaffold a new app inside the offline_viewer folder. Run

yo electron

You can fill in the questions after executing the above command as applicable. Once the project is scaffolded and dependencies are installed, we will add a few more modules applicable to the offline viewer. Run,

npm install cheerio diskdb request --save

  • cheerio is to manage DOM manipulation in Nodejs. This module will help us sandboxing the content.
  • diskdb for data persistence.
  • request module for contacting the wordpress blog and get the posts as well as to sandbox images.
  • for realtime communication between the locally persisted data and the UI.

For generating installer for mac & some folder maintenance, we will add the below two modules.

npm install trash appdmg --save-dev

The final package.json should look like

Do notice that I have added bunch of scripts and updated the meta information of the project. We will be using NPM itself as a task runner to run, build and release the app.

To make sure everything is working fine, run

npm run start

And you should see

Screen Shot 2015-05-27 at 6.16.23 pm

Build the Socket Server

Now, we will create the server interface for our offline viewer, that talks to the WordPress JSON API.

Create a new folder named app at the root of the project. Inside the app folder, create two folders named serverclient. This folders kind of visually demarcate the server code vs. the client code. Here the server being Nodejs & client being Angular application. Inside the Electron shell, any code can be accessed any where, but to keep the code base clean and manageable, we will be maintaining the above folder structure.

Inside the app/server create a file named server.js. This file is responsible for setting up the socket server. Open server.js and update it as below

Things to notice

Line 1: We require the getport module. This module takes care of looking for an available port on the user’s machine that we can use to start the socket server. We cannot pick 8080 or 3000 or any other static port and assume that the selected port would be available on the client. We will work on this file in a moment.

Line 2 : We require the fetcher module. This module is responsible for fetching the content from WordPress REST API, save the data to DiskDB and send the response back.

Line 3 : We require the searcher module. This module is responsible for searching the locally persisted JSON data, as part of the search feature.

Line 7 : As soon as we get a valid port from getport module, we will start a new socket server.

Line 11 : Once a client connects to the server, we will setup listeners for load event and search event.

Line 13 : This event will be fired when the client wants to get the posts from the server. Once the data arrives, we emits a loaded event with the posts

Line 19 : This event will be fired when the client send a query to be searched. Once the results arrive, we emit the results event with the found posts.

Line 27 : Once the socket server is setup, we will execute the callback and send the used port number back.

Next, create a new file named getport.js inside the app/server folder. This file will have the code to return an unused port. Update getport.js as below

Things to notice

Line 2 : Require the net module, to start a new server

Line 3 : Starting value of the port, from which we need to start checking for a available port

Line 5 : A recursive function that keeps running till it finds a free port.

Line 10 : We attempt to start a server on the port specified, if we are successful, we call the callback function with the port that worked else, if the server errors out, we call the getPort()  again. And this time, we increment the port by one & then try starting server. This goes on till the server creation succeeds.

Next, create a file named fetcher.js inside app/server folder. This file will consist of all the business logic for our application. Update app/server/fetcher.js as below