Ensuring Consistent Code in JavaScript Apps

18 March 2020

Ensuring code consistency in JavaScript Apps is made a lot easier these days with the advent of easy to use static analysis tools, formatters, bundlers, shareable configuration, package management and more.

How I like to ensure consistent code is by leveraging a few of these things in a few key places to make it both painless to set up and mostly impossible to avoid.

Step 1. Static Analysis

Static analysis is the use of a tool such as ESLint, StyleLint, PHPCS. These tools will analyse your code in a static form (i.e. not while running), and compare it to a configuration file that you provide to ensure that it meets your predefined standards.

For a JavaScript app, this usually means ESLint with one of the popular ESLint configurations, and an NPM script that gets run from time to time. But it can be made even easier and more real time than that. Many of the most popular text editors amongst JavaScript developers have plugins that integrate ESLint into the editor and can provide real time feedback as you code.

Step 2. Formatters

This is often a point of contention as many static analysis tools can also do the job of a formatter, however, I believe that the use of specific tools for specific jobs is the appropriate way forward. Which means that I am a big fan of Prettier.

Prettier is an opinionated code formatter with minimal configuration options that works with a range of different types of code - JavaScript, CSS, HTML, Markdown, YAML, PHP and more. Much like ESLint, there are plugins available for many of the most popular editors that can format your code on save.

Step 3. Bundlers

How do bundlers help make code more consistent? They encourage the modularisation of your codebase, encouraging you to group code in logical units that can be imported and exported to other parts of your application. If this is done well it can make code more DRY by encouraging re-use of existing code over repeated implementations.

They have other benefits, of course, such as minification, cache busting, source map generation, tree-shaking, and much more, but those aren’t primarily related to code consistency.

Step 4. Package Management

Package management is inextricably intertwined with code bundling. Of course, we had various forms of package management before we truly had bundlers but bundlers make package management much more useful.

Instead of having to write and maintain your own implementation of a particular package you can install, import, and use other peoples code lessening your maintenance overhead. Many popular packages are written and maintained by groups of highly skilled developers and put through their paces by thousands of developers every day, ensuring that bugs are minimal and often resolved quickly.

Step 5. Shareable Config

Something that package management makes very simple to do is sharing configuration for the tools already mentioned. Many people are used to using things like the AirBNB ESLint config, but often never think about making their own config useable by others.

It’s highly unlikely that you’ll be using whatever config you decide to extend exactly as it’s written. Eevery time you set up a new project you’ll need to reconfigure your app to use your preferred config.

But there’s another way - publish your config. All a published config is, is a collection of rules being enabled or disabled - including extending other shared configs. Share your config and then it’s only an NPM install away. For you, and for others.

Step 6. Making It Mandatory

Something that I haven’t touched on until now is enforcing the use of these tools in projects. Most of them are either command line tools, editor plugins, or NPM scripts, but all of those need to be manually run so why not automate it?

There are a number of ways this you can automate it.

You could have a continuous integration server that runs all of these tools on your code every time you push a commit. Or use a CI service like TravisCI, or Github Actions. But these are not immediate, slow, potentially expensive, and don’t actually help protect inconsistent code from getting into your git history.

Another way is to add a githook that runs every time you want to commit or push. It’s a really solid solution, but now you’ve got to maintain another piece of code that isn’t specific to your project or product.

My preferred way is to use a tool like Husky or Lint-staged. These use githooks under the hood but abstract all the maintainance away. They can run any command you choose across either your whole codebase or just the staged files, and can be configured with just a few lines in your package.json file.

And it doesn’t have to just be the tools I’ve already mentioned. Why not run your tests, or confirm that git history hasn’t diverged, or, or, or…

Step 7. Abstract it all away

Once you’ve reached this point, you’re likely pretty happy with your setup. You’ve got your code being linted, formatted, and modularised all very nicely, but you’ve still got all the config files sitting around making your code base look busier than it needs to.

Why not hide it all? Why not create a package that wraps it all up nicely and exposes just a couple of entries that you can add to your package.json file. It can handle the dependency management, the configuration, the installation, and just about everything else to do with keeping these tools running. Which leaves you with just an NPM install to get everything working exactly how you want it.

There are even some packages out that that you can use as is or base your own on. Ones like kcd-scripts, or (tooting my own horn here) dfhscripts. There’s also react-scripts built in to create-react-app which is much more opinionated and less extensible.


Something that you may or may not have noticed is that I haven’t used the word quality in this post at all. That’s because these tools don’t guarantee quality code, they guarantee consistent code.

It is entirely possible to use all of these tools and have consistent poor quality code.

Enforcing consistency is automatic, quality is up to you.