stylis

What is stylis?

The stylis npm package is a lightweight CSS preprocessor that allows developers to write nested CSS, use mixins, and perform other transformations before the CSS is compiled. It is particularly designed to be used with CSS-in-JS libraries and offers a middleware architecture to extend its capabilities.

What are stylis's main functionalities?

CSS Preprocessing

Stylis allows you to write nested CSS rules, which it will then flatten into valid CSS. The code sample demonstrates how to preprocess a nested CSS string.

const stylis = require('stylis');

const css = `
  .parent {
    color: red;
    .child {
      color: blue;
    }
  }
`;

const output = stylis('.parent', css);
console.log(output);

Prefixing

Stylis automatically adds vendor prefixes to CSS rules when necessary. The code sample shows how to automatically prefix the 'display: flex;' rule.

const stylis = require('stylis');

const css = `display: flex;`;

const output = stylis('', css);
console.log(output);

Middleware

Stylis supports middleware, allowing you to intercept and transform CSS at various stages of processing. The code sample demonstrates a middleware that changes the color property for elements with the class '.button'.

const stylis = require('stylis');

stylis.use((context, content, selectors, parents, line, column, length) => {
  if (context === 2 && selectors[0] === '.button') {
    return content.replace('color: red', 'color: blue');
  }
});

const css = `.button { color: red; }`;

const output = stylis('', css);
console.log(output);

Other packages similar to stylis

postcss

PostCSS is a tool for transforming CSS with JavaScript plugins. It is more established and has a larger ecosystem of plugins compared to stylis. PostCSS can be used for a wide range of tasks including linting, optimization, and applying polyfills.

sass

Sass is a mature and feature-rich CSS extension language that allows for variables, nesting, mixins, and more. Unlike stylis, Sass has its own syntax and requires compilation to CSS, but it offers a more comprehensive set of features for styling.

less

Less is another CSS pre-processor that extends the capabilities of CSS with variables, mixins, functions, and more. It is similar to Sass and offers a different syntax and feature set compared to stylis.

README

Stylis

• ~1Kb minified+gzipped
• ~3kb minified

Stylis is a small css compiler that turns this

stylis('#user', styles);

Where styles is the following css

// flat css
font-size: 2em;
font-family: sans-serif;

// polyfill for shadow dom selectors
:host {
    color: red;
}

:host(.fancy) {
    color: red;
}

:host-context(body) {
    color: red;
}

// removes line comment

.name {
    transform: rotate(30deg);
}

// inject to global scope
@global {
    body {
        background: yellow;
    }
}

// inject to global scope inline
span, h1, :global(h2) {
	color:red;

	/**
	 * removes block comments
	 */
}

// prefixing
& {
	animation: slidein 3s ease infinite;
    display: flex;
    flex: 1;
    user-select: none;
}

// namespaced animations
&:before {
	animation: slidein 3s ease infinite;	
}

// namespaced keyframes
@keyframes slidein {
	from { transform: translate(10px); }
	to { transform: translate(200px); }
}

// flat namespaced css in @media
@media (max-width: 600px) {
    display: block;

	&, h1 { 
        appearance: none; 
    }
}

// nested
h1 {
    color: red;

    h2 {
        display: block;

        h3, &:hover {
            color: blue;
        }
    }

    font-size: 12px;
}

into this (minus the whitespace)

#user {
	font-size: 2em;
	font-family: sans-serif;
}
#user {
    color: red;
}
#user.fancy {
    color: red;
}
body #user {
    color: red;
}
#user .name {
    -webkit-transform: rotate(30deg);
    -ms-transform: rotate(30deg);
    transform: rotate(30deg);
}
body {
    background: yellow;
}
#user span,
#user h1,
h2 {
    color: red;
}
#user {
    display: -webkit-flex;
    display: flex;

    -webkit-flex: 1;
    -moz-flex: 1;
    flex: 1;

    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;

    -webkit-animation: userslidein 3s ease infinite;
    animation: userslidein 3s ease infinite;
}
#user:before {
    -webkit-animation: userslidein 3s ease infinite;
    animation: userslidein 3s ease infinite;
}
@-webkit-keyframes userslidein {
    from {
        -webkit-transform: translate(10px);
        -ms-transform: translate(10px);
        transform: translate(10px);
    }
    to {
        -webkit-transform: translate(200px);
        -ms-transform: translate(200px);
        transform: translate(200px);
    }
}
@keyframes userslidein {
    from {
        -webkit-transform: translate(10px);
        -ms-transform: translate(10px);
        transform: translate(10px);
    }
    to {
        -webkit-transform: translate(200px);
        -ms-transform: translate(200px);
        transform: translate(200px);
    }
}
@media (max-width: 600px) {
    #user, #user h1 {
        -webkit-appearance: none;
        -moz-appearance: none;
        appearance: none;
    }

    #user {
        display: block;
    }
}

h1 {
    color: red;
    font-size: 12px;
}

h1 h2 {
    display: block;
}

h1 h2 h3,
h1 h2 h2:hover {
    color: blue;
}

Supports

• Edge
• IE 9+
• Chrome
• Firefox
• Safari
• Node.js

---

Installation

direct download

<script src=stylis.min.js></script>

CDN

<script src=https://unpkg.com/stylis@0.8.3/stylis.min.js></script>

npm

npm install stylis --save

API

stylis(
    selector: {string}, 
    cssString: {string}, 
    namespaceAnimations, {boolean}
    namespaceKeyframes {boolean}
);

// namespaceAnimations and namespaceKeyframes allow 
// you to prevent keyframes and animations
// from being namespaced

Intergration

You can use stylis to build an abstraction ontop of, for example imagine we want to build an abstract that makes the following React Component possible

class Heading extends React.Component {
    stylesheet(){
        return `
            &{
                color: blue
            }
        `;
    }
    render() {
        return (
            React.createElement('h1', 'Hello World')
        );
    }
}

We could simply extend the Component class as follows

React.Component.prototype.stylis = function (self) {
    var namespace = this.displayName;

    return function () {
        stylis(namespace, self.stylesheet(), document.head);
        mounted = true;
        this.setAttribute(namespace);
    }
}

Then use it in the following way

class Heading extends React.Component {
    stylesheet(){
        return `
            &{
                color: blue
            }
        `;
    }
    render() {
        return (
            React.createElement('h1', {ref: this.stylis(self)}, 'Hello World')
        );
    }
}

When the first instance of the component is mounted the function assigned to the ref will get executed adding a style element with the compiled output of stylesheet() where as only the namespace attribute is added to any subsequent instances.

You can of course do this another way

class Heading extends React.Component {
    constructor (props) {
        super(props);
        // or you can even inline this
        this.style = React.createElement('style', {id: this.displayName}, this.stylesheet());
    }
    stylesheet(){
        return `
            &{
                color: blue
            }
        `;
    }
    render() {
        return (
            React.createElement('h1', null, 'Hello World', this.style)
        );
    }
}

One will add it to the head another will render it in place with the component.

If you want a better picture into what can be done, there is an abstraction i created for dio.js that does away with the above boilerplate entirely http://jsbin.com/mozefe/1/edit?js,output