Write beautiful and consistent JavaScript code using ESLint, Prettier and VSCode

Write beautiful and consistent JavaScript code using ESLint, Prettier and VSCode

Write beautiful and consistent JavaScript code using ESLint, Prettier and VSCode - A short and simple tutorial Bring consistency across your JS code and teams

Write beautiful and consistent JavaScript code using ESLint, Prettier and VSCode - A short and simple tutorial Bring consistency across your JS code and teams

Proper code styling and formatting is a must for every project and even more so when you have multiple developers working on same codebase. With so many additions to JavaScript following the ECMA standards and different ways to perform a same task there need to be unified standards in your project on what to choose. You will find recommendations all over the internet on what to prefer but still there is no strict rule on what to use. For instance, you may choose to create variables using var instead of the JavaScript’s newlet keyword for scope based variables. So it is upto you to set rules for your project so that every developer on the team follows them and there is consistency across all your code. Here’s where code linting comes into play.

What are linters?

A linter is a program that analyses your source code for possible programmatic and styling errors. Different languages have different linters. ESLint is the linter for JavaScript. Since JavaScript is an interpreted language it is extremely useful to have programmatic errors pointed out before running the application. Here is a programmatic error that ESLint will catch and report to you:

let myFunction = () => {};
myFuction(); // A typo causing error at runtime

For styling errors, ESLint allows you to set rules specific to your project. If you deviate from those rules when writing code ESLint will report them to you. To check out the entire list of rules that ESLint supports follow this link:

List of available rules

Hey, that’s not what I came for, I wanted ESLint setup already.#### Setting up ESLint is super easy.

First we need to install ESLint as a dev dependency:

npm install eslint --save-dev

Next we initialise ESLint for our project:

./node_modules/.bin/eslint --init 

You will then be asked a few questions regarding your preferences to configure ESLint and at the end .eslintrc will be generated.

If you are unsure about the questions you can skip this step. Instead just create .eslintrc manually.

At this point, you have a working ESLint setup for your project. The default ESLint configuration uses rules from eslint:recommended config. However, there is a better alternative in my opinion: eslint-config-airbnb.

Airbnb has created a predefined set of ESLint rules based on Airbnb JavaScript Style Guide. This is an extremely useful resource for all JavaScript developers and tries to establish a common ground for good JS practices. They have reasoned every decision they have taken and give you a chance to understand the same. To get started install the following npm packages as dev dependency:

// For react projects

//For non react projects

Next you need to edit your .eslintrc to extend from Airbnb config. This is how your config would look like:

Also note that you can still write custom rules that will override Airbnb config rules by specifying them in the rules block.

Now ESLint is setup for your project and you can lint your files by running this command: ./node_modules/.bin/eslint [fileName] which will give you an output similar to this:

Great! You can now have consistent code in your project that adheres to the rules you have set up. But we talked about properly formatted code as well, where is that?

Enter, Prettier

Prettier is an opinionated code formatter that has predefined rules for code formatting and indentation. To use prettier in your project run the following command:

npm install --save-dev prettier

This will give you access to Prettier CLI and you can check and perform auto-formatting through a single command:

./node_modules/.bin/prettier --write [fileName]

This command will run prettier on the file and reformat the code. Convenient, isn’t it. Just make sure all your previous changes are saved since this command directly writes to file.

Another good thing about prettier is that it can be configured to use with ESLint wherein it uses eslint rules for code formatting and we can see prettier formatting errors in a file when we run eslint on that file.

**Using Prettier with ESLint **

First you need to install the following npm packages as dev dependency:


Next we need to configure ESLint to use prettier, so we make the necessary changes to .eslintrc In this case, we just need to add "plugin:prettier/recommended" to the extends block. Combining with our previous configuration the final extends block will look something like this :

"extends": ["airbnb", ""plugin:prettier/recommended""]

Now, you will get Prettier errors included in ESLint errors. The above setup is editor independent and does not require the use of extensions.

We have come far to make our code consistent and beautiful. However, if you noticed, there is no efficiency in this process. We have to run ESLint and prettier on each file through the terminal. For ESLint errors we need to fix the errors and run ESLint again to verify. Well, that is why we have text editors and VSCode is one of the best at it.

VSCode for efficiency

VSCode has extensions for ESLint and Prettier that automate the entire process for you without the need of a CLI. Firstly install these two extensions:

When you restart VSCode and have the above setup for ESLint and Prettier completed, you should be able to see the magic happen. The ESLint errors are now directly visible in the editor without the need of running command through terminal.

You can hover over the red lines to view what the error is. Even better, you can look at the Problems panel in VSCode to get details of all errors present in a file.

Prettier works out of the box as well. Just press cmd + shift + P to open the VS Code commands box and click Format Document and you will have prettified code. Another useful addition is auto-format on save. Click cmd + , to open VSCode settings and add this line to workspace settings: "editor.formatOnSave":true

Now every time you save your file it will automatically be prettified.

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:


First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?


I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI