Switching to UnoCSS

My website has always been the breading ground for new tech. I've been using this website for testing out new tools and
I write about them if they are worth writing about, one such tool is Unocss. This post will be a deep dive on why I am
migrating to unocss.

CSS Utilities

First let's understand what is a css utility. Css Utilties or also known as atomic css is a way of defining small reusable classes,
that has a very little functionality. For example,

.p-1 {
  padding: 1px;
}
.p-5 {
  padding: 5px;
}
.p-10 {
  padding: 10px;
}

As you can see from the above code, we have separate css for each value of padding. So instead of defining css manually
everytime, you can simply define these helper css or use an existing css utility framework. I've been
working with a lot of such utitlity frameworks, and people have their own utilty css'. Some of the famous css utility
frameworks are Tailwind Css, Windi Css and Tachyons
etc. So basically these utility frameworks will have a list of helper classes which provide basic css functionalities.

Old-school way

The traditional way of using a css utility or helper is to build one yourself, that is what we (@Facilio)
were doing, when I joined. Like we would have our own helper css files which will have hundreds of utility css. Based on the
requirement we might add new classes. As you guessed, this is a lot of work and our production bundle had all
those css files even if certain classes weren't used. This is when I came across tailwind.

The Problem

I've been using tailwind css a lot, both in my personal projects as well as in work related ones. This seemed to
solve the initial problem we had of defining and maintaining all the inbuilt helper css'. Tailwind was good, but
I started facing problems when I had to use css properties that are not part of tailwind's utility css. Like for example,
let's say you want to give a padding exactly of 210px (to match certain design constraints), you can't do it in tailwind,
you can either use p-52 (208px) or use p-56 (224px). You can fix this by providing this special css property in
tailwind config, but this method won't scale as we can't keep adding custom css properties, this defeats the purpose of
using a utility css framework.

// tailwind.config.js
module.exports = {
  theme: {
    padding: {
      DEFAULT: '1px',
      '0': '0',
      '2': '2px',
      '3': '3px',
      ....
      '54': '210px' // <-- here
    }
  }
}

Another issue I faced with tailwind was that, tailwind was shiping it's entire utility classes
in our production build which affected the app's performance. Also I was working on multiple microfrontends at that
time and each one had a lot of these unwanted css utilities which made the issue even worse. After searching through
their docs I came across a concept they had called Purging which ships only the used css classes,
but this seems to only work in production and I still have to work with all those utility css during development.

This is where frameworks like Windi comes into play, they are similar to tailwind css, but they have a lot of utility
css classes compared to tailwind and they are on demand. I really like Windi's on-demand way of doing things. Traditional css
frameworks would generate the css' and then they would use the required ones in the production build. This might affect
your app's performance because of unecessary computations (since we are generating the css and are not using them). But
the on-demand way would first scan for the css classes you are using and then generate only those in our builds.

Thus I was able to solve the problem of removing unwanted css in my builds, but I still couldn't use custom css classes
(even in Windi CSS). To do so I had to override their config with a butt load of information, which was a lot to do for
a simple functionality.

The Solution

UnoCSS unlike other css frameworks is a css engine without any utility css of it's own, rather it uses different css framework's
presets. They generally work with build tools and after mentioning the preset you like you can use that framework's classes
in your projects right away. Guess what, you can give any number of presets or write your own preset and use it with UnoCSS.
And like Windi CSS they use the on demand way of generating css. I am using next js in this website so the build tool used
in next is webpack, also I was using tailwind with postcss previously, so the migration looks something like this,

Configuring UnoCSS with Next Js

First you can remove all the tailwind and postcss config files from your project, then remove the following packages,

{
  "autoprefixer": "^10.2.6", // remove
  "postcss": "^8.3.5", // remove
  "tailwind": "^2.2.4" // remove
}

Then add the following dependencies,

npm i @unocss/preset-uno @unocss/preset-web-fonts @unocss/webpack unocss -D

Now add a unocss config file and a next js config file (If you never had one like me before),

// unocss.config.js
import presetAttributify from "@unocss/preset-attributify";
import presetUno from "@unocss/preset-uno";
import { defineConfig } from "unocss";

export default defineConfig({
  presets: [presetUno(), presetAttributify()],
});

// next.config.js
const UnoCSS = require("@unocss/webpack").default;

const nextConfig = {
  reactStrictMode: true,
  webpack: (config) => {
    config.plugins.push(UnoCSS());
    config.cache = false; // have to be false for hmr
    return config;
  },
};

module.exports = nextConfig;

Now import the uno.css file in /_app.js file and use tailwind / windi css class names to see the magic.
You can add other frameworks presets or add a custom one also, check out their docs
to see on how to add your own custom presets. Apart from presets UnoCSS has a few other advantages,

• You can write your own custom rules / classes, like you can add the following for a custom border css,

rules: [["my-custom-border", { border: "solid 1px pink" }]];

Dynamic Rules

You can also add dynamic rules by using regex,

rules: [
  [/^m-(\d+)$/, ([, d]) => ({ margin: `${d / 4}rem` })],
  [/^p-(\d+)$/, (match) => ({ padding: `${match[1] / 4}rem` })],
];

• You can also change the order of precedence in which the styles should be applied, like in the following configuration border-1 is applied or has higher precedence than border-2 if used together,

shortcuts: {
  "border-1",
    { border: "solid 1px pink" },
    "border-2",
    { border: "solid 1px green" };
}

• Also you can add custom css resets by installing @unocss/reset. If you use UnoCSS along with other CSS frameworks, they probably already do the resetting for you. If you use UnoCSS alone, you can use resetting libraries like Normalize.css.