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https://github.com/samwillis/x-style

x-style (Extract Style) - A Tiny Inline Nested CSS Library
https://github.com/samwillis/x-style

css nested-css style tailwind tailwindcss

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x-style (Extract Style) - A Tiny Inline Nested CSS Library

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# x-style (Extract Style) - A Tiny Inline Nested CSS Library



x-style is a tiny library that adds full css support to inline styles, allowing you to

define style where they are being used with the new nested syntax. It does this by extracting

inline stiles from your html on the fly:



```html



  Hello World



```



See the [demo](http://samwillis.co.uk/x-style/) for more examples.



The styles are only parsed once so *repeated use of the same style is very fast*, the

library adds an attribute to each element for use by a css selector to find the

styles and apply them. Repeated use of the same `x-style` value uses the sate generated

stylesheet. If you add additional elements or change styles after the page 

loads the library will automatically find and update the styles.



x-style is tiny, as little as 1.8kb with the un-nest plugin or 856 bytes without,

and designed to be pasted directly into your html, this ensures that it runs 

synchronously, as your pages loads, with no FOUC (flash of unstyled content).



In the newest browsers - Chrome 112+, Safari 16.5+ and Firefox 117+ - the nested styles work

without any extra code, but for "older" browsers you need to use the `x-style-unnest.js`

plugin. See https://caniuse.com/css-nesting.



There is a [small benchmark](http://samwillis.co.uk/x-style/benchmark/run.html) that shows 

for a typical tailwind page with about 400 style classes the overhead of x-style is about 

5ms on load.



## Why?



Utility class toolkits like Tailwind have shown that defining styles inline can be

better than using a css file. It encapsulated the style with the component, making it 

easier to understand and maintain, this is known as 

["locality of behaviour"](https://htmx.org/essays/locality-of-behaviour/). 

When used in combination with a component based framework it results in a very clean 

and maintainable code.



However, increasingly these frameworks are implementing more and more css as classes, 

creating a domain specific language shoehorned into the css class system that is not 

easy to understand. The aim of x-style is to allow this locality of behaviour, but by 

using native css syntax. Additionally these toolkits require separate tooling or build 

steps, neither of which are needed with x-style.



x-style is the ideal companion to tools such as [htmx](http://htmx.org) and 

[Alpine.js](http://alpinejs.dev).



## How to use



The recommended minimal setup is to add this to your `` directly before ``:



```html



// x-style core:

(()=>{var r=document,f=(e,t)=>e.querySelectorAll(t),h=[],b=[],e=(a,i)=>{var e,

o="",s=0,n=new Map,l=a+"-match",t=new MutationObserver(e=>{for(var t of e)if(

"attributes"===t.type)d(t.target);else if("childList"===t.type)for(

var r of t.addedNodes)r instanceof HTMLElement&&(r.hasAttribute(a)&&d(r),[...f(r

,`[${a}]`)].forEach(d));u()}),u=()=>{o&&((e=r.createElement("style")

).innerHTML=o,r.head.appendChild(e),e=null,o="")},c=(e,t)=>{var t=l+"-"+n.get(t)

,r="__"+l;return e[r]&&e.removeAttribute(e[r]),e.setAttribute(t,""),e[r]=t},

d=e=>{var t,r=e.getAttribute(a);!r||n.has(r)?i||c(e,r):(n.set(r,++s),

t=i?`[${a}="${CSS.escape(r)}"]`:`[${c(e,r)}]`,h.forEach(e=>r=e(r)),

t+=` { ${r} }`,b.forEach(e=>t=e(t)),o+=t+"\n")};f(r,`[${a}]`).forEach(d),u(),

t.observe(r.documentElement,{attributes:!0,attributeFilter:[a],childList:!0,

subtree:!0})};e.pre=h,e.post=b,e.version="0.0.3",window.xstyle=e})();

// x-style unnest plugin:

(()=>{var c=CSS.supports("selector(&)"),r=window.xstyle,e=r=>{if(c)return r;

r=r.replace(/\/\*[^*]*\*+([^/][^*]*\*+)*\//g,"");for(var e,t,s,a="",p="",h=0,

i="",l=r.length,n=[],o=[],u=()=>{i.match(/\S/)&&(p+=n[n.length-1]+"{"+i+"}",i=""

)};h<l;)"\\"===(s=r[h])?(a+=r.slice(h,h+2),h+=2):(";"===s?(i+=a+s,a=""

):"}"===s?(i+=a,a="",u(),o.pop()?p+=s:n.pop()):"{"===s?(u(),e=n[n.length-1],(t=a

).match(/^\s*@/)?(o.push(!0),p+=t+s):(e&&(t=((t,r)=>{var e,s=r.match(/^\s*/)[0],

a=r.match(/\s*$/)[0],p=0;for(t=t.trim(),r=r.trim();p<t.length;)if("\\"===(e=t[p]

))p+=2;else if('"'===e||"'"===e){var h=e;for(p++;e!==h;)p+="\\"===(e=t[p])?2:1;

p++}else if("("===e)for(var i=1;")"!==e&&0<i;)"("===(e=t[p])&&i++,")"===e&&i--,

p++;else{if(","===e){t=":is("+t+")";break}p++}return s+[...r.match(

/(\\.|[^,])+/g)].map(r=>{var e=(r=r.trim()).replace(/(^|[^\\])(&)/g,"$1"+t);

return e=e===r?t+" "+r:e}).join(", ")+a})(e,t)),n.push(t),o.push(!1)),a=""):a+=s

,h++);return p};r.post.push(e),r.unnest=e})();

// Activate x-style with the "x-style" attribute:

xstyle("x-style");



```



This is both the core x-style code and the unnest plugin. The `xstyle("x-style")`

activates the library, it will find all elements with the `x-style` attribute and

process their styles.



Alternatively you can link to the x-style code and plugins directly, however as they are

tiny it is better, and faster, to inline them.



There is an optional second boolean parameter that disables adding a `x-style-match` 

attribute to the elements that have had their styles applied. Instead the naked 

`x-style` attribute value if used for the selector, but this can be quite slow. As the 

defualt behavour mutates the DOM it may cause problems with some frameworks, if so set 

this to `true` to disable the behaviour.



```js

xstyle("x-style", true);

```



See below for details on activating the `envvar` and `@apply` plugins.



Finally, you can also load it from a cdn:



```html



xstyle("x-style");



```



## Plugins:



There are a number of tiny plugins that add extra functionality to x-style. At a minimum

you probably want to use the `x-style-unnest.js` plugin to add support for "old"

browsers - well most browsers - that don't support nested styles.



Plugins are loaded by adding the plugins code to the page `` directly after the

x-style code.



### x-style-unnest.js



The unnest plugin adds support for old browsers that don't support nested styles. It 

does this by parsing the style and unnesting it, so the above example would be 

converted to:



```css

div[x-style-match-1] {

  color: red;

  font-size: 30px;

}

div[x-style-match-1]:hover {

  background-color: yellow;

}

div[x-style-match-1] > span {

  color: green;

}

```



It also supports the `@media`, `@supports` and other `@` rules, correctly promoting

the "at" rules to the top level.



The implementation is not perfect, but it works well enough for most cases. This is

intentional so as to keep the code small and fast. An alternative would be to used

a browser build of postcss, but that would be about 100kb (100x the size of x-style) 

and async, resulting in a flash of unstyled content.



### x-style-envvar.js



The envvar plugin adds support for custom 

[environment variables](https://developer.mozilla.org/en-US/docs/Web/CSS/env)

in styles. As it's not possible to use `var()` in media queries (custom properties are 

part of the cascade and require a DOM node which media queries don't have), this plugin 

adds support for defining custom environment variables which are then substituted in 

your css. Custom environment variables are planned for css, but there is not yet any 

standard for defining them.



You define custom environment variables for x-style via js like this:



```js

xstyle.env = {

  "--my-break-point": "800px",

};

```



You can then use the custom environment variables in your css like this:



```css

@media (min-width: env(--my-break-point)) {

  /* ... */

}

```



Note that this implementation of environment variables does not update the css when the

value changes.



To use the plugin, add the following to the x-style `` in the `<head>`

immediately after the x-style code but before the `xstyle("x-style")` call:



```html

(()=>{var r=window.xstyle;r.env=r.env||{},r.pre.push(e=>{for(var n,t,i,l=r.env,

p=[...e.split(/\senv\((--[^),]+)/g)];1<p.length;)n=p.pop(),t=p.pop().trim(),

")"===n[0]?n=n.slice(1):","===n[0]&&([i,n]=n.split(")",2)),void 0!==l[t]?p[

p.length-1]+=" "+l[t]+n:p[p.length-1]+=i?" "+i.slice(1).trim()+n:" "+n;return p[

0]})})();

```



### x-style-apply.js



The apply plugin implements `@apply`, extracting the css rules from the class defined in

the current document and inserting then into the new css.



So, if you have a class defined like this:



```css

.my-class {

  color: red;

}

```



You can then use it like this:



```html

<div

  x-style="

  &:hover {

    @apply my-class;

  }

"

>

  Hello

</div>

```



This is not a official standard, and is unlikely to be, but it's a very useful feature. 

However it is recommended that you use `var()` instead as it's a standard.



To use the plugin, add the following to the xstyle `<script>` in the `<head>`

immediately after the xstyle code but before the `xstyle("x-style")` call:



```html

(()=>{var s=/@apply ([^;}$]*);?/g,n={},t=e=>{if("."!==e[0]&&(e="."+e),n[e]

)return n[e];var s=[];for(const t of document.styleSheets)for(

const r of t.cssRules)r.selectorText===e&&s.push(r);return s.map(e=>{e=e.cssText

return e.slice(e.indexOf("{")+1,e.lastIndexOf("}"))}).join(" ")};

xstyle.pre.push(e=>e.replace(s,(e,s)=>s.split(" ").map(t).join(" ")))})();

```