html-by-css

Generate html by writing css.

Install

npm i html-by-css

Usage

import generate from 'html-by-css';

const source = `
  ul#list {
    list-style: none;
    margin: 0;
    padding: 0;

    & li.item*3 {
      padding: .5rem;

      :is(a[href="#"]) {
        content: Link;
        color: inherit;
      }
    }
  }
`;

const { html, css } = generate(source);

HTML

<ul id="list">
  <li class="item">
    <a href="#">Link</a>
  </li>
  <li class="item">
    <a href="#">Link</a>
  </li>
  <li class="item">
    <a href="#">Link</a>
  </li>
</ul>

CSS

/* legacy: false (default) */
ul#list {
  list-style: none;
  margin: 0;
  padding: 0;
  & li.item {
    padding: .5rem;
    :is(a[href="#"]) {
      color: inherit;
    }
  }
}

/* legacy: true */
ul#list {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul#list li.item {
  padding: .5rem;
}

ul#list li.item :is(a[href="#"]) {
  color: inherit;
}

How it works

• Use postcss to parse and walk through source.
• On target nodes, process data as HTML:
  • Find content on non-pseudo elements and inject as text.
  • Find emmet syntax and duplicate elements.
  • Parse selector using css-what.
  • Transform selector to himalaya schema.
• Process source as valid CSS:
  • Remove content on non-pseudo elements.
  • Remove emmet syntax.
  • Optionally, use postcss-nesting plugin to transform into legacy, non-nested CSS.
  • Apply additional plugins as provided.
• Return object with { html, css }.

Features

Nesting

The nesting should be prepared using the current w3 CSS Nesting specification. The most important concept is that a nested selector must start with a symbol.

.foo {
  /* ❌ invalid */
  span {
    color: hotpink;
  }

  /* ✅ valid */
  & span {
    color: hotpink;
  }

  /* ❌ invalid */
  span & {
    color: hotpink;
  }

  /* ✅ valid */
  :is(span) & {
    color: hotpink;
  }
}	

If you wish to collapse the nesting for the CSS output, set legacy: true in the options. This uses postcss-nesting with the default options.

const { html, css } = generate(source, { legacy: true });

If you want to set your own options, provide your own version of the postcss-nesting plugin and configure.

import nesting from 'postcss-nesting';
import generate from 'html-by-css';

const postcssPlugins = [nesting({
  noIsPseudoSelector: true
})];
const { html, css } = generate(source, { plugins: postcssPlugins });

Warning

Do not use legacy: true with your own postcss-nesting configuration. The internal (legacy) usage will run first. Either do not declare or explicitly set legacy: false. This is only when using a custom postcss-nesting, all other plugins can be used with legacy: true.

PostCSS plugins

You can include additional postcss plugins. Example below helps with removing duplicate declarations.

import dedupe from 'postcss-discard-duplicates';
import generate from 'html-by-css';

const postcssPlugins = [dedupe()];
const { html, css } = generate(source, { plugins: postcssPlugins });

This is helpful if you have several similar elements with different contents.

ul#list {
  & li.item {
    & a*0 {
      color: inherit;
    }

    & a[href="/home"] {
      content: Home;
    }

    & a[href="/about"] {
      content: About;
    }

    & a[href="/contact"] {
      content: Contact
    }
  }
}

Note

The use of a*0 says write the styles found here, but don't write HTML. When you use this, the represented node and it's children will not be written as HTML.

Duplicate nodes

To create multiple elements, use emmet syntax.

ul {
  li*5 {
    /* Makes 5 <li/> elements */
  }
}

This li*5 selector is not valid CSS and is transformed during processing to li.

Text content

To add text content, use the content property on non-pseudo elements.

main {
  & h1 {
    content: Hello world!;
  }
}

<main>
  <h1>Hello world!</h1>
</main>

Note

There are no quotes around the string. Adding quotes would include the quotes in the output.

The content property is not valid on non-pseudo elements and is removed from these declarations during processing.

Testing

npm t

• Using cheerio to traverse HTML in tests.
• Using @projectwallace/css-analyzer to analyze returned CSS.

There's definitely some cases not covered in the tests yet.

• content prop and nested selector (both text and children).
• Other pseudo-selectors (:nth-child(), :checked).

Why

Your scientists were so preoccupied with whether they could, they didn't stop to think if they should.

There's a few projects out there that are HTML preprocessors (Haml, Pug) which have their own (sometimes CSS-like) syntax. I wondered if we could get closer to just writing CSS to produce HTML. With the new nesting specification and the power of postcss, it looks like we can!