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highlighted-code

A textarea builtin extend to automatically provide code highlights based on one of the languages available via highlight.js.

Live demo

<!doctype html>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<style>
textarea[is="highlighted-code"] { padding: 8px; }
</style>
<script type="module">
(async ({chrome, netscape}) => {

  // add Safari polyfill if needed
  if (!chrome && !netscape)
    await import('https://unpkg.com/@ungap/custom-elements');

  const {default: HighlightedCode} =
    await import('https://unpkg.com/highlighted-code');

  // bootstrap a theme through one of these names
  // https://github.com/highlightjs/highlight.js/tree/main/src/styles
  HighlightedCode.useTheme('github-dark');
})(self);
</script>
<textarea is="highlighted-code"
          cols="80" rows="12"
          language="javascript" tab-size="2" auto-height>
(async ({chrome, netscape}) => {

  // add Safari polyfill if needed
  if (!chrome && !netscape)
    await import('https://unpkg.com/@ungap/custom-elements');

  const {default: HighlightedCode} = await import('https://unpkg.com/highlighted-code');

  // bootstrap a theme through one of these names
  // https://github.com/highlightjs/highlight.js/tree/main/src/styles
  HighlightedCode.useTheme('github-dark');
})(self);
</textarea>

API

The component is literally a textarea so everything that works or applies for this kind of element works and applies for this custom element too.

The only extras attributes this component offer are:

  • language, reflected as area.language to define which kind of language should be highlighted. See the list of supported languages here (see those that don't require extra packages).
  • tab-size, reflected as area.tabSize, to determine the amount of virtual spaces covered by tabs. Because we live in a Mobile world, the default is 2.
  • auto-height, reflected as area.autoHeight, to render the textarea as if it was a regular element. See the test page as example, or set autoHeight = true in the live demo and see the area growing while typing.

The exported HighlightedCode default class exposes these public methods/accessors:

  • HighlightedCode.useTheme(name:string) to bootstrap any valid CSS theme by name. This can also be a fully qualified URL to avoid CDN when desired.
  • HighlightedCode.insertText(text:string) to programmatically insert some text where the selection is.
  • HighlightedCode.library:hljs a getter to retrieve the imported hljs library, usable to register missing PLs or do something else.

Exports

The main export uses all default languages included in highlight.js, but there are other variants:

  • highlighted-code/web, which includes only Markdown, JS, TS, JSON, CSS, and HTML or XML
  • highlighted-code/sql, which includes only SQL

These variants are much lighter than default module.

F.A.Q.

How to disable editing?

You can either textarea.disabled = true or:

<textarea is="highlighted-code" language="css" disabled>
textarea[is="highlighted-code"]::before {
  content: "it's that simple!";
}
</textarea>
How to disable spellcheck?

You can either textarea.spellcheck = false or:

<textarea is="highlighted-code" language="css" spellcheck="false">
textarea[is="highlighted-code"]::before {
  content: "it's that simple!";
}
</textarea>
How to set cols or rows?
<textarea is="highlighted-code" language="css" cols="40" rows="12">
textarea[is="highlighted-code"]::before {
  content: "it's that simple!";
}
</textarea>
How to set a placeholder?
<textarea is="highlighted-code" language="css"
          placeholder="write css..."></textarea>
How to ...?

Look, this is a custom element builtin extend.

If you know how and when to use a textarea, you're 90% done with this module.

Now you need just the is attribute with value highlighted-code, a language attribute with a supported language from highlight.js library, optionally a tab-size attribute to have tabs wider than 2, and a theme, where default would work too, as long as HighlightedCode.useTheme('default') is invoked.

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A textarea builtin extend to automatically provide code highlights based on one of the languages available via highlight.js

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