jscodeshift and codemods

JS Code Shift

JS Code shift is a toolkit for running codemods, codemods are transforms that take existing code file(s) and produces new code. That is a codemod in the simplest form. I like to think if them as find and replace script on steroids. JS code shift created by Facebook provides 2 things:

  • Runner: The runner executes the transform scripts and provides feedback on the files changed
  • A wrapper for recast, recast is a AST-to-AST tool. Recast is used to preserve the style and syntax of the code that was transformed.

The pattern for running a codemod is to provide the transform path then path to the file(s) that you wish to transform.


jscodeshift -t path-to-codemod path-to-code 


You can also provide additional options to help with the process e.g. -d for a dry run if you want to test without making changes. -p to print detailed info on the process. JS Code Shift provides an API for transforms


module.exports = function(fileInfo, api) {
  return api.jscodeshift(fileInfo.source)

This example taken from the repo, shows how you can easily replace all occurrences of a foo variable with bar. The above transform get passed the file and the JS Code Shift API. This is then used to get the file source and from here there are methods to get different parts of the file e.g. findVariableDeclarators.



JS Code Shift provides an extremely powerful toolkit but the true power lives in the code mods that have been created.  I have managed to find some from quick googling, the reactjs community repo holds a collection react code mods. With react being a fast paced and evolving library code mods really help to evolve an existing code base to new patterns and methodologies. Pattern changes such as React.render to ReactDOM.render, in react 0.14 the render method was moved to the react-dom package. Instead of manually changing all your files you could use the code mod. Other code mods are provided such as  manual-bind-t0-arrow which replaces all manuall function binding to use ES6 arrow functions which scopes the functions.

Code Mods are not only just for react they can be run on any JavaScript code, such as a code mod to help migration to ES6. Removing all var’s and replacing with let or const can be a challenge when you have a large code base but running a code mod makes the process quick and painless.

Taking old ES5 code using var’s

Running the codemod:

Resulting code:

We can see here that the codemod has checked the code and determined that the new source should have one let and two const’s.  However nothing is ever perfect and we could say that the const for myObj should be a let, although the code is still technically valid.


You can find more codes mods in the following repos:


Should You Commit Compiled Code?

Working on a Java project you would never dream of committing a built war or jar file, so when working with JavaScript why would you think of committing the compiled source. So many projects I have worked on have by default commit the dist/lib code. This adds bloat and unnecessary steps to committing and merging such as making sure that you build before committing files and that you build when merging.

Preventing Commits of Complied Code

When setting up a new project always create a .gitignore file and add this to the project. For most projects I have worked on we have always used a dist/lib folder for the compiled source. For these cases add the following to your .gitignore.

# compiled source

if you have already committed the dist or lib you can stop tracking the files by using the following git command: git rm -r –cached

How to Provide Users with the Compiled Source

The easiest and most recommended (personal opinion) method for distributing your source is via npm. Npm allows you to publish code to a central repository and allow users to quickly access and use the code. The reason that I prefer Npm over other package managers like bower is due to the Npm repository, the repository allows publishers to push only the needed content so that users only pull down and have access that what they need. Bower however acts more like a link to git repositories which in turn requires publishers to commit complied source.

NPM Publish

To publish to Npm you can follow some simple steps that will have you pushing code in no time.
Create your npm account. You can also pay to have private repositories and push/get from these.
– Add the name field to the package.json file in your project.
– Add a prepublish task to the npm scripts
– Run npm publish

You can see an example file below:

  "name": "module-name",
  "version": "10.3.1",
  "description": "An example module to illustrate the usage of a package.json",
  "author": "Your Name ",
  "scripts": {
    "test": "echo 'No Tests'",
    "start": "node index.js",
    "prepublish": "uglifyjs --compress --mangle input.js"
  "main": "dist/foo.js",

You can either have a build task that you call from the prepublish or just call the build commands. Now when you run npm publish the prepublish will run and compile your source. Now you need to make sure that only this gets pushed to the Npm repository. This can be achieved by using a .npmignore similar to the .gitinore however this will list all your project content except for the dist/lib folders.

Now your project is setup to only publish and track what users need and want.


JavaScript Developers Toolkit

My tool kit has grown over the years and even more so since I became a focused and dedicated JavaScript developer. From development environments, online resources and third party tools.
## IDE
As JavaScript does not require compiling you could write it all in notepad or any basic text editor as the browser will handle the code. But when developing large scale JavaScript applications you need more tools and features from your IDE.

My IDE of choice is WebStrom when I worked on Java based projects I used Intellij and it was a dream to use which made WebStrom the only option for me. The feature set was above par to any other development environment I had used. Features such as intellisense (which is extremely powerful), being able to find method usages and definitions, code quality checking and auto refactoring, source control tools built in like merging, a built in terminal, debugging for not only client side JavaScript, NodeJS and even Grunt and Gulp. I also blogged before about the power of the keybindings in WebStrom/Intellj

However this does come at a cost, there are a number of great free alternatives such as Sublime Text, Atom, Aptana Studio, Komodo Edit to name a few. Each with a different set of features, pros and cons.

Third Party Apps

So you have an IDE but there are other apps out there that can aid the developer. Two I use on a daily bases are SIP colour picker and LICEcap.


SIP is a powerful colour picker that will work anywhere on the screen and provide colours in a number of different formats to suit any development needs. It also keeps track of the most recent colours you have picked.


LICEcap is a tool for generating gif files from recording your screen, this comes in useful when developing UI components and trying to share these with other developers. When documenting a UI code base I always add a gif of the UI component in action. An alternative to LICEcap is Record It however this tool auto uploads the gif which is not great if you are working with internal products or products that have not been released yet.

Online Tools

Ove the years I have built up a collection of online tools or reference sites that I use on a daily basis’s. Here are some:


JSFiddle is probably one of the most known online tools for web developers, it allows you to create online projects with just one html, css and JavaScript file, however you can add third party code files. This is a great tool for sharing code examples when either getting help/advice or showing off some new code or feature. There has also recently been a release of a ES6 Fiddle to allow for online editing of ES6 code.

JS Bin

JSBin is almost the same as JSFiddle however has some extra features such as a console panel. The main reason I use JS Bin is when I cant get some code to work in JSFiddle I double check on JSBin to remove any doubts. I have also experienced some issues with JSFiddle and company proxy servers blocking the output of the Fiddle.

Code Pen

Code Pen is probably one of the best looking out of the code playgrounds, It seems to be more focused on the look and feel of code. If you check the examples pages there are some beautiful examples of JavaScript and CSS. The interface is clean and simple also which works well when you want to focus on the code at hand.

JS Perf

JS Perf is a JavaScript performance testing site allowing you to pit different methods of doing the same action against each other and see which one out preforms the other. I use this a lot in work when dealing with different patterns and even different methods from different libs. I have used it before when testing the performance of lodash vs underscore vs jQuery vs ES5.

Reference Tools

Having all the tools are great but not knowing how to develop or how to over come bugs makes all the tools useless.

MDN (Mozillia Developer Network)

MDN is a great site for looking up not only JavaScript but HTML and CSS API documentation the site also provides news and examples. An example of the API documenatation can be found n the Flexbox page, the page provides information on the API, examples and the browser compatibility.

Dev Docs

Dev Docs is a must have tab open in your browser. If you work with JavaScript you most likely work with a few frameworks, you will at some point have to look into the docs for that framework. Dev docs pull in all the JavaScript frameworks that you want and keeps them in one handy tab. With the ablitiy to search and save for offline use it will save you some much time. You can open github issues to get other frameworks added.

Keeping up with the Joneses

If you are into JavaScript you most likely have realised that the world of JavaScript moves fast and you need to find ways to keep up. Here are some methods and resources I use:


JavaScript Jabber

JavaScript Jabber is a weekly podcast that discusses font and backend JavaScript, coding best practices, coding environments and the JavaScript community. The podcast has covered a very wide range of topics with regular guest from big name companies and communities from Angular and ember core developers to Brendan Eich (which was my favourite show to date).


In very simple terms NodeUp is a weekly podcast is a about Node.js, each week a different aspect of node is looked at usually with guests who are closely related to the topic and can provide a deep insight into the technology. With big name guests from the likes of Netflix, Socket IO developers and even the people behind NPM.

Shop Talk

Shop Talk is a weekly front end development podcast that has a mix-up of shows with guests from the tech world and shows for answering listener submitted questions.

The Changelog

The Changelog podcast s not just for web development but does contain a lot for the web developer. Each week a core developer of a tool or framework talks about the progression of the project where it has been where its going.

News Feeds / Twitter Accounts

I use Reddit for most of my JavaScript news needs, the following subreddits are vey usefull:

  • /r/angularjs
  • /r/backbonejs
  • /r/css
  • /r/emberjs
  • /r/Frontend
  • /r/HTML
  • /r/javascript
  • /r/marionettejs
  • /r/Meteor
  • /r/mongodb
  • /r/node
  • /r/programmingtools
  • /r/reactjs
  • /r/rubyonrails
  • /r/WatchPeopleCode

Twitter can also be a great resource if you follow the correct accounts:

  • https://twitter.com/paul_irish
  • https://twitter.com/addyosmani
  • https://twitter.com/davidwalshblog
  • https://twitter.com/jashkenas


### JavaScript: The Good Parts
The must read JavaScript book, I first read this when I got into JavaScript development. I still keep a copy on my desk almost 7 years later. This book covers the basics of JavaScript a sets you up to be a great developer.

Learning JavaScript Design Patterns

This is a great book to move onto after the good parts as it takes you though the different design patterns and best practices in JavaScript. The book helps you understand JavaScript in a way that allows you to develop large applications and become better at managing code.

High Performance JavaScript

This is a nice book to keep around for reference on how to make your code as performant as possible. There are some really useful concepts that can help any level of developer.


This has been a detailed look at the JavaScript developers toolkit, every developer knows what works best for them and so some of the tools I mentioned might not be for you. Your toolkit is never complete so new tools will come and go, if you have something that helps you work or find useful in some way drop a comment.

This post has been powered by Genesis – Turn it On Again and Finca Filadelfia


Chrome Dev Tools – IDE Replacement

I recently talked at locally JavaScript meetup I talked about the top 5 features of the Chrome developer tools. I have given a simular talk at my old company which talked through the dev tools and how they can be used to improve the development process.

After the first talk it started to dawn on me that with some of the features in the tool kit you could get to the point of replacing the development IDE. The development cycle can be a comfortable or painful process for a developer, I have worked on some projects where the time between making a code change and seeing the results could take up to 5 minutes.

So how do we streamline this process, enter Chrome developer tools. The most powerful feature in the sources pannel.

Chrome Source Panel

As the complexity of JavaScript applications increase, developers need powerful debugging tools to help quickly discover the cause of an issue and fix it efficiently. The Chrome DevTools include a number of useful tools to help make debugging JavaScript less painful.

The sources panel provides all the needed tools for developing;
– breakpoints
– call stack
– watches
– console execution
– live editing of code

This is all great but we are still only in the dev tools, we still need a IDE or text editor to create the code then open it in chrome. What if we could edit the code and not have return the to IDE to make the changes again.

Well we can, dev tools allows you to map files to a local workspace. This makes a link between the files in the browser to the files on you local machine. See this in action below:

Adding a workspace

Now that the workspace is linked you can make changes in the browser and have these saved to the local file, this now breaks the link between the IDE and the browser. You have created a instant feadback loop.

This shows the power of the Chrome developer tools, this is only the start. As time progresses the dev tools will grow it’s feature set providing more options for developers. If you have any cool tips or tricks for the dev tools please leave a comment.


JetBrains Intellij Workshop

Today I attended a workshop from the team at Jetbrains, the workshop gave a detailed look into the Intellij IDE. The workshop was presented by Hadi Hariri, with his anti mouse philosophy in mind we dug into the ways to using Intellij to work efficiently. I will outline some of the take away points that I felt that most developers would not know and must learn if you plan to use or already use Intellij to develop.


“use the keyboard” the mantra that Hadi repeated and which made me feel bad for all the times I’v used the mouse.

Presentation assistant was shown at the point as Hadi would be using the keyboard to do everything we would need to see what key combinations were being executed. Presentation assistant flashes up on screen what keys are used to carry out an action and the action name. This will now be turned on anytime that I do live coding demos and you should do the same. This feature should also be turned on while you are pair programming for the times when you are bashing away on the keyboard and the other developer is lost to the world trying to work out what the you are doing.

So now on to the meat of the workshop the hip cool key combinations that will make you look L33T in front of all you programming friends.

cmd + o get to class
cmd + 1 open the project structure
– In the project structure you can also:
– start typing and this will search for the file
– set auto scroll so that files opened via search are scrolled to on the project view
shift (double press) search everywhere this will search not only classes but files, build tasks, features anything you can really think about.
In this feature you can also toggle IDE features
Run build configurations
cmd + 7 file structure of the project
cmd + n create new file
– in the new file selection you can also start typing to search/refine the selection
cmd + e show recent file
– this comes into play especially if you disable tabled editing, Hadi was an advocate of the one tab rule in which you only have one file open at as time and using the file navigation built into Intellij you can go back and forth. Tab settings can be changed from the general settings menu and any limit can be set on the number of open tabs.
shift + cmd + e show recently edited files
cmd + y show a popup window of the code definition
cmd + b go to the code definition

shift + cmd F12 hide all windows except the file you are editing

alt + up select line (context aware) e.g. select var, then function the class etc
shit cmd enter statement complete can be used to complete if statements

###Refactoring Code
import preferences allows you to import a namespace or each individual class, you can also add tolerances to if more that say 3 classes are used from a package then you can import the package.
cmd + t surround code, allowing you to surround a statement easily

These are just some of the tips and tricks that I had picked up from the workshop, the help documentation built into Intellij and the web site is a great resource for looking for shortcuts and different approaches for completing a task. A big thanks to the team at Dev Bash for setting up the workshop, check them out for more talks and workshops like this.

If you have learnt any tips or tricks for using this very powerful IDE please leave a comment.