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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

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Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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HTML 

              
                <div>
  <button>Generate Fact</button>
</div>
<ul></ul>
!

CSS 

              
                body {
  background-color: #333;
  color: #DDD;
  font-size: 21pt;
  padding: 1em;
}
div {
  text-align: center;
}
button {
  border: 1px solid currentColor;
  background-color: transparent;
  color: currentColor;
  font-size: inherit;
  border-radius: 3px;
  box-shadow: 1px 1px 2px 1px black;
  cursor: pointer;
}
button:hover {
  box-shadow: inset 1px 1px 2px 1px black;
}
ul {
  list-style-type: none;
  padding: 0;
}
li {
  border-bottom: 1px solid currentColor;
  padding: 1em;
}
!

JS 

              
                console.clear();
let raw = `Did you know that (
    the ( Fall | Spring ) Equinox |
    the ( Winter | Summer ) ( Solstice | Olympics ) |
    the ( Earliest | Latest ) ( Sunrise | Sunset ) |
    Daylight ( Saving | Savings ) Time |
    Leap ( Day | Year ) |
    Easter |
    the ( Harvest | Super | Blood ) Moon |
    Toyota Truck Month |
    Shark Week )
(
    happens ( earlier | later | at the wrong time ) every year |
    drifts out of sync with the (
        Sun |
        Moon |
        Zodiac |
        ( Gregorian | Mayan | Lunar | iPhone ) Calendar |
        atomic clock in Colorado ) |
    might ( not happen | happen twice ) this year )
because of (
    time zone legislation in ( Indiana | Arizona | Russia ) |
    a decree by the pope in the 1500s |
    ( precession | libration | nutation | libation | eccentricity | obliquity ) of the (
        Moon |
        Sun |
        Earth's axis |
        equator |
        prime meridian |
        ( international date | mason-dixon ) line ) |
    magnetic field reversal |
    an arbitrary decision by ( Benjamin Franklin | Isaac Newton | FDR ) )
? 
Apparently (
    it causes a predictable increase in car accidents. |
    that's why we have leap seconds. |
    scientists are really worried. |
    it was even more extreme during the (
        Bronze Age. |
        Ice Age. |
        Cretaceous. |
        1990s. ) |
    there's a proposal to fix it, but it (
        will never happen. |
        actually makes things worse. |
        is stalled in congress. |
        might be unconstitutional. ) |
    it's getting worse and no one knows why. )`;

function pickOptions(string){
  return string.replace(/\s+\(\s*( [^()]+)\s*\)/g, (_all, options) =>
    options
      .split(/\s*\|/)
      .sort(() => Math.random() - 0.5)[0]
  );
}

function run() {
  const li = document.createElement('li');
  list.prepend(li);
  let previousResult = "";
  let result = pickOptions(raw.replace(/\s+/gm, ' '));
  while (result != previousResult) {
    previousResult = result;
    result = pickOptions(previousResult);
  }
  li.textContent = result.replace(/(\w) ([.,,?])/g, "$1$2");
}

const button = document.querySelector('button');
const list = document.querySelector('ul');
button.addEventListener('click', run);
run();
!
999px

Console