Setting up Webpack + Babel + ReactJS

I started using Webpack module bundler recently and thought I would document some of my learning. In the past couple of posts I wrote about bundling JavaScript projects using Browserify module bundlers. Webpack can be used as a replacement for Browserify; but it has some nice additional features like bundling of static files and code splitting.

This post is not meant to be tutorial on Webpack, I just wanted to describe how to configure Webpack, specifically using Webpack loaders for Bablel and ReactJS. I will show how to build a JS project using standalone Webpack and also using Webpack APIs in Gulp. The project is available on Github at

Module Dependencies

Node packages required to build the project are, of course, in package.json. If you are using above starter project from Github, then run ‘npm install’ to install all the required packages. Else make sure you install all the packages listed in devDependencies of package.json . The list contains babel, required babel presets for ES6 and ReactJS, webpack and webpack-dev-server, webpack loaders for babel, LESS and CSS.

Webpack Configuration

Webpack configuration is specified in webpack.config.js. This config file is read when you run webpack or webpack-dev-server command. Optional gulpfile.js (to build the project using Gulp) also loads this file and passes to Webpack APIs.

Here is a brief description of some of the entries in the config file – Continue reading “Setting up Webpack + Babel + ReactJS”

Using ReactJS with Babel and ES6

I wanted to create this post shortly after the last post about Setting up ES6+Babel+Gulp, but it got delayed for some reasons. Anyways ..

Though it is not very complicated to setup ReactJS to work with Babel, there are a few non-obvious things you need to be aware of, specifically the absence of  auto-binding in ReactJS when coded in ES6. Let’s create a small NodeJS project using Gulp –

Install following packages –

npm install gulp gulp-connect vinyl-source-stream browserify babelify babel-preset-es2015 react react-dom babel-preset-react --save-dev

In addition to packages installed in the last post, here we are installing react, react-dom and babel-preset-react packages.

The directory structure is similar to one in the previous post, except that we add views folder for JSX files.

  -- build
  -- src
    -- js
       -- views
    -- html
  -- gulpfile.js

Gulp ‘build’ task is modified to add ‘react’ preset to babelify and add jsx extension to browserify (we want browserify to process .jsx files in addition to .js files) Continue reading “Using ReactJS with Babel and ES6”

Setting up ES6+Babel+Gulp

ECMAScript 6 (ES6, specification at has many nice features, but presently not all browsers support ES6. However you can still develop your applications in ES6 and make it run in all browsers. For this you need what is called as transpiler – which converts ES6 code to ES5, which all browsers understand currently.

One of the popular transpiler is Babel . In this post we will see how to use Node.js (, Gulp.js (, Browserify (  to compile ES6 code to ES5.

Gulp is a build tool for Node.js applications. Browserify resovles ‘require’ modules of Node.js and bundles all modules in one file. We will first use browserify to combine all our JS code in one file and then feed the output to babelify to translate the code to ES5. Structure of this sample project is as follows –

  -- build
  -- src
    -- js
    -- html
  -- gulpfile.js

Not all the files are folders are shown above, for example package.json and node_modules folder are not shown.

Continue reading “Setting up ES6+Babel+Gulp”

Using JavaScript Promises with Cordova

JavaScript Promises

JavaScript Promises could make asynchronous programming a bit easier. Most of the APIs of Cordova are asynchronous. So when you want to call one asynchronous API after the other, you have to nest API in the callback functions of the previous API. Many APIs also take error handler as one of the parameter to API function. At some point the whole code could become very difficult to read and maintain.

JS Promises  could make this a bit simpler. Promise is an object, which takes a function callback with two arguments, resolve and reject. Promise represent a value that would be resolved sometime in future, it is is not already resolved or rejected. The promise can be rejected explicitly or when any JavaScript exception is thrown. See and Promises on MDN for details on JS Promises. Advantages of Promises is realized when you need to chain multiple asynchronous calls. Promises can also be useful if you want to guarantee then a piece of code is executed only once. Promises are executed only once. Continue reading “Using JavaScript Promises with Cordova”

Encrypting data with Crypto-JS in JavaScript

I have been working intermittently on a HTML5 mobile application for some time now. This application stores some sensitive date locally (it is a standalone mobile application) and I did not want to store the data in clear text. I wanted to make retrieval of data difficult to some extent, if the device ends up in the wrong hands. So the data had to be encrypted. The application code is in JavaScript, so I started looking for a JS library that can encrypt data. I found that Crypto-JS met my requirements and it was easy to use too.

Before I proceed further, I must confess that my knowledge of encryption and digital security in general is very basic. So the solutions discussed in this post may not be the best in terms of protecting the data.

As I said, Crypto-JS is very simple to use. You can use different cipher algorithms like AES. DES etc. and APIs are simple. e.g. to encrypt using AES , you would call –

encryptedData = CryptoJS.AES.encrypt(textToEncrypt, secretPhrase); //include aes.js script

In the above API, the first argument to encrypt function is text data you want to encrypt, e.g. password. The second argument is a secret phrase (also called passPhrase). This could be any text. Secret phrase is the key that is used to encrypt the data. However you will have to use the same key (secret phrase) when decrypting the data. Continue reading “Encrypting data with Crypto-JS in JavaScript”

Parsing JavaScript code using Mozilla Rhino

Last year I had blogged “Understanding AST created by Mozilla Rhino parser“, where I exaplained how to traverse AST to get all functions and variables. Since then I have received some comments, public and private, to provide sample code. So here is an example of how to parse JavaScript code and get all functions and variables using Mozilla Rhino.

Note that my intention here is not to build the complete symbol table for any given JavaScript code. And I have not run a lot of test cases on this code. The idea is to show how AST could be traversed and how hierarchy of symbols (functions and variables) be built .

So, for example, if you feed following JavaScript code to this program –

function func1()
	var local1 = 10;

	global1 = 20;

obj1 = {
	objFunc1 : function()
		var local2 = 30;
	objProp1 : "prop1"

You will get following output –

Function : func1
		Function : objFunc1

Yes, I know there are duplicates for object and closure – because they are first processed as variable names and then object/closure. This can be easily fixed, but I am going to leave it that way to keep the code simple. Continue reading “Parsing JavaScript code using Mozilla Rhino”

Framework for interacting with embedded WebView in iOS application

Last year around the same time I had written a post about Calling Objective-C code from JavaScript in iOS applications . I created a simple framework for it and described how to use it in that post.

Recently I was working on an application that required WebView to be embedded in the same View Controller along with other native iOS controls. I decided to use the above framework, but knew that  my ViewController class will have to extend WebViewController class of the framework. Though I could have done that, I thought separating the functionality of UIWebViewDelegate from the WebViewController would be a better design. So I replaced WebViewController with WebViewDelegate which implements UIWebViewDelegate protocol. I also removed getInitialPageName method from WebViewInterface.h . So here are the files in the new framework – Continue reading “Framework for interacting with embedded WebView in iOS application”

Sprite Animation Revisited

Last year I had blogged about animating sprite using Kinetic JS.
Code in that post was part of a simple game I had created. So the code specific for animating sprite was explained in snippets. A reader of that post contacted me with a request to provide a complete example. So I created a small demo of sprite animation only. If you are interested, you can download it from here. This demo animates images in the sprite sheet at a fixed location, it does not move the image. So I thought  it would be interesting to add motion to sprite images when they are animated.

First, take a look at the demo. Click on the Walk button to make the person walk. You can stop any time. If the person hits right side wall, then she falls, which is also simulated using sprite animation. I know the ‘walk’ does not look natural, but creating graphics is not my string point and this is the best I could manage.

Walking Speed : (Enter value from 1 to 10)

Continue reading “Sprite Animation Revisited”

Calling Objective-C code from JavaScript in iOS applications

In the last post I described how to Create iOS Application with HTML User Interface . In this post I am going to describe how to access Objective-C code from JavaScript running in the WebView. It is not as easy as it is in Android. There is no direct API in UIWebView to call native code, unlike in Android which provides WebView.addJavascriptInterface function.

However, there is a work-around. We can intercept each URL before it is being loaded in the WebView. So to call the native code, we will have to construct a URL and pass method name and argument as part of the URL. We then set this URL to window.location in the JavaScript and intercept it in our ViewController.
However most examples I have seen (including PhoneGap) create an instance of iframe and set its source to the URL –
Continue reading “Calling Objective-C code from JavaScript in iOS applications”

Get/Set local variables of JavaScript function from outside & Dynamic code insertion in JS function

I am working on a JavaScript framework that needs to get list of local function variables and set values of some of them. Unlike Java, JavaScript does not have runtime introspection
support. In Java you can do this using Java Reflection APIs, but I couldn’t think of any way to do this in JavaScript. So I searched on the web and came across two threads of discussions on StackOverflow –

There are some interesting solutions discussed in the above threads. The first one discusses solutions for setting local variable values. The second one interested me because I found the technique useful for injecting code (that will set local variable value) in a function.

Continue reading “Get/Set local variables of JavaScript function from outside & Dynamic code insertion in JS function”