Compile CSS classes on demand with Tailwind CSS JIT mode

Recently Tailwind CSS has added an experimental new compiler that you can use to generate its classes. If you aren't familiar with how Tailwind works traditionally, here's the summary; based on the options you provide in a tailwind.config.js file, on build time Tailwind will create all the necessary classes for your code. Then, when building for production, it will remove any unused classes with PurgeCSS.

The new Just-In-Time mode now uses this same method to create instead of remove classes. This has amazing benefits for Tailwind like a reduced build time in development and production, as well as allowing for the stacking of variants. Althoughm I think a more interesting usage is the creation of arbitrary classes. Let's go through an example of where this would be useful.

Say I'm creating a series of social media icons on my website using SVGs, where I want each icon to be its brand colours. There's a couple of ways this could be done normally. (I'll be using React for this example but the same applies to HTML or any other framework)

You could use inline styles:

<Twitter style={{ color: "#00acee" }} />

Or an external stylesheet:

/* styles.css */
.twitter-color {
  color: #00acee;
}

<Twitter className="twitter-color" />

Or you could even add the colour to your Tailwind theme:

// tailwind.config.js
module.exports = {
  /* ... */
  colors: {
    twitter: "#00acee",
  },
  /* ... */
};

<Twitter className="text-twitter" />

While these solutions work, they're not ideal. There may be other circumstances in your code where you might need to position a background image or set the height of navigation, and writing a precise pixel value in your usual Tailwind styles would be the easiest way.

That's where Just-In-Time mode comes in:

<Twitter className="text-[#00acee]" />

By putting any value in square brackets, the just in time compiler will create a new class on the fly using this value. To use it you need to be using Tailwind CSS 2.1 or later and then you can add mode: 'jit' to your config file, as well as ensuring you have the purge option setup.

You can read more about this feature in Tailwind's documentation.