svelte-highlight

Syntax highlighting for Svelte using highlight.js.

Documentation

Installation

# npm
npm i svelte-highlight

# pnpm
pnpm i svelte-highlight highlight.js

# Bun
bun i svelte-highlight

# Yarn
yarn add svelte-highlight

Note that pnpm users must also install highlight.js.

Basic Usage

The Highlight component requires two props:

code: text to highlight
language: language grammar used to highlight the text

Import languages from svelte-highlight/languages.

See SUPPORTED_LANGUAGES.md for a list of supported languages.

<script>
  import Highlight from "svelte-highlight";
  import typescript from "svelte-highlight/languages/typescript";

  const code = "const add = (a: number, b: number) => a + b;";
</script>

<Highlight language={typescript} {code} />

Styling

Import styles from svelte-highlight/styles. See SUPPORTED_STYLES.md for a list of supported styles.

There are two ways to apply highlight.js styles.

Injected styles through svelte:head
CSS StyleSheets

Injected Styles

This component exports highlight.js themes in JavaScript. Import the theme from svelte-highlight/styles and inject it using the svelte:head API.

<script>
  import Highlight from "svelte-highlight";
  import typescript from "svelte-highlight/languages/typescript";
  import github from "svelte-highlight/styles/github";

  const code = "const add = (a: number, b: number) => a + b;";
</script>

<svelte:head>
  {@html github}
</svelte:head>

<Highlight language={typescript} {code} />

CSS StyleSheet

Depending on your set-up, importing a CSS StyleSheet in Svelte may require a CSS file loader. SvelteKit/Vite automatically supports this. For Webpack, refer to examples/webpack.

<script>
  import { Highlight } from "svelte-highlight";
  import typescript from "svelte-highlight/languages/typescript";
  import "svelte-highlight/styles/github.css";

  const code = "const add = (a: number, b: number) => a + b;";
</script>

<Highlight language={typescript} {code} />

Linking from a CDN

CSS StyleSheets can also be externally linked from a Content Delivery Network (CDN) like unpkg.com.

Warning

Using a CDN is best suited for prototyping and not recommended for production use.

HTML

<head>
  <link
    rel="stylesheet"
    href="https://unpkg.com/svelte-highlight/styles/github.css"
  />
</head>

svelte:head

<svelte:head>
  <link
    rel="stylesheet"
    href="https://unpkg.com/svelte-highlight/styles/github.css"
  />
</svelte:head>

Svelte Syntax Highlighting

Use the HighlightSvelte component for Svelte syntax highlighting.

<script>
  import { HighlightSvelte } from "svelte-highlight";
  import github from "svelte-highlight/styles/github";

  const code = `<button on:click={() => { console.log(0); }}>Increment {count}</button>`;
</script>

<svelte:head>
  {@html github}
</svelte:head>

<HighlightSvelte {code} />

Auto-highlighting

The HighlightAuto component uses the highlightAuto API and attempts to guess what grammar to use based on the provided code.

Warning

Auto-highlighting will result in a larger bundle size. Specify a language if possible.

<script>
  import { HighlightAuto } from "svelte-highlight";
  import github from "svelte-highlight/styles/github";

  const code = `body {\n  padding: 0;\n  color: red;\n}`;
</script>

<svelte:head>
  {@html github}
</svelte:head>

<HighlightAuto {code} />

Line Numbers

Use the LineNumbers component to render the highlighted code with line numbers.

<script>
  import Highlight, { LineNumbers } from "svelte-highlight";
  import typescript from "svelte-highlight/languages/typescript";
  import atomOneDark from "svelte-highlight/styles/atom-one-dark";

  const code = "const add = (a: number, b: number) => a + b";
</script>

<svelte:head>
  {@html atomOneDark}
</svelte:head>

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers {highlighted} />
</Highlight>

Hidden Border

Set hideBorder to true to hide the border of the line numbers column.

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers {highlighted} hideBorder />
</Highlight>

Wrapped Lines

By default, overflowing horizontal content is contained by a scrollbar.

Set wrapLines to true to hide the border of the line numbers column.

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers {highlighted} wrapLines />
</Highlight>

Custom Starting Line Number

The line number starts at 1. Customize this via the startingLineNumber prop.

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers {highlighted} startingLineNumber={42} />
</Highlight>

Highlighted Lines

Specify the lines to highlight using the highlightedLines prop. Indices start at zero.

Use --highlighted-background to customize the background color of highlighted lines.

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers
    {highlighted}
    highlightedLines={[0, 2, 3, 14]}
    --highlighted-background="#000"
  />
</Highlight>

Custom Styles

Use --style-props to customize styles.

Style prop	Description	Default value
--line-number-color	Text color of the line numbers	`currentColor`
--border-color	Border color of the column of line numbers	`currentColor`
--padding-left	Left padding for `td` elements	`1em`
--padding-right	Right padding for `td` elements	`1em`
--highlighted-background	Background color of highlighted lines	`rgba(254, 241, 96, 0.2)`

<Highlight language={typescript} {code} let:highlighted>
  <LineNumbers
    {highlighted}
    --line-number-color="pink"
    --border-color="rgba(255, 255, 255, 0.2)"
    --padding-left={0}
    --padding-right="3em"
    --highlighted-background="#000"
  />
</Highlight>

Language Targeting

All Highlight components apply a data-language attribute on the codeblock containing the language name.

See SUPPORTED_LANGUAGES.md for a list of supported languages.

[data-language="css"] {
  /* custom style rules */
}

Language Tags

Set langtag to true to display the language name in the top right corner of the code block.

Customize the language tag background, color, and border-radius using style props.

See the Languages page for a list of supported languages.

Style prop	Description	Default value
--langtag-top	Top position of the langtag	`0`
--langtag-right	Right position of the langtag	`0`
--langtag-background	Background color of the langtag	`inherit`
--langtag-color	Text color of the langtag	`inherit`
--langtag-border-radius	Border radius of the langtag	`0`
--langtag-padding	Padding of the langtag	`1em`

<script>
  import { HighlightAuto } from "svelte-highlight";

  $: code = `.body { padding: 0; margin: 0; }`;
</script>

<HighlightAuto {code} langtag />

<HighlightAuto
  {code}
  langtag
  --langtag-background="linear-gradient(135deg, #2996cf, 80%, white)"
  --langtag-color="#fff"
  --langtag-border-radius="6px"
  --langtag-padding="0.5rem"
/>

Custom Language

For custom language highlighting, pass a name and register function to the language prop.

Refer to the highlight.js language definition guide for guidance.

<script>
  import { Highlight } from "svelte-highlight";
  import hljs from "highlight.js";

  const language = {
    name: "custom-language",
    register: (hljs) => {
      return {
        /** custom language rules */
        contains: [],
      };
    },
  };
</script>

<Highlight {language} code="..." />

Custom Plugin

Additional plugin languages can be installed and used separately.

This example uses the cURL language plugin.

<script>
  import { Highlight } from "svelte-highlight";
  import curl from "highlightjs-curl";
  import github from "svelte-highlight/styles/github";

  const language = {
    name: "curl", // Language name displayed in the langtag
    register: curl,
  };

  const code = `curl -X POST "https://api.example.com/data" \\
     -H "Content-Type: application/json" \\
     -d '{"key": "value"}'`;
</script>

<svelte:head>
  {@html github}
</svelte:head>

<Highlight {language} {code} />

Code-splitting

You can use the await import syntax for code-splitting.

In the example below, the HighlightAuto component and injected styles are dynamically loaded.

<script>
  import { onMount } from "svelte";

  let component;
  let styles;

  onMount(async () => {
    component = (await import("svelte-highlight")).HighlightAuto;
    styles = (await import("svelte-highlight/styles/github")).default;
  });
</script>

<svelte:head>
  {#if styles}
    {@html styles}
  {/if}
</svelte:head>

<svelte:component
  this={component}
  langtag
  code={`body {\n  padding: 0;\n  color: red;\n}`}
/>

Component API

`Highlight`

Props

Name	Type	Default value
code	`any`	N/A (required)
language	{ name: `string`; register: hljs => `object` }	N/A (required)
langtag	`boolean`	`false`

$$restProps are forwarded to the top-level pre element.

Dispatched Events

on:highlight: fired after code is highlighted

<Highlight
  language={typescript}
  {code}
  on:highlight={(e) => {
    /**
     * The highlighted HTML as a string.
     * @example "<span>...</span>"
     */
    console.log(e.detail.highlighted);
  }}
/>

`LineNumbers`

Props

Name	Type	Default value
highlighted	`string`	N/A (required)
hideBorder	`boolean`	`false`
wrapLines	`boolean`	`false`
startingLineNumber	`number`	`1`
highlightedLines	`number[]`	`[]`

$$restProps are forwarded to the top-level div element.

`HighlightSvelte`

Props

Name	Type	Default value
code	`any`	N/A (required)
langtag	`boolean`	`false`

$$restProps are forwarded to the top-level pre element.

Dispatched Events

on:highlight: fired after code is highlighted

<HighlightSvelte
  {code}
  on:highlight={(e) => {
    /**
     * The highlighted HTML as a string.
     * @example "<span>...</span>"
     */
    console.log(e.detail.highlighted);
  }}
/>

`HighlightAuto`

Props

Name	Type	Default value
code	`any`	N/A (required)
langtag	`boolean`	`false`

$$restProps are forwarded to the top-level pre element.

Dispatched Events

on:highlight: fired after code is highlighted

<HighlightAuto
  {code}
  on:highlight={(e) => {
    /**
     * The highlighted HTML as a string.
     * @example "<span>...</span>"
     */
    console.log(e.detail.highlighted);

    /**
     * The inferred language name
     * @example "css"
     */
    console.log(e.detail.language);
  }}
/>

Name		Name	Last commit message	Last commit date
Latest commit History 829 Commits
.github/workflows		.github/workflows
examples		examples
playwright		playwright
scripts		scripts
src		src
tests		tests
www		www
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
LICENSE		LICENSE
README.md		README.md
SUPPORTED_LANGUAGES.md		SUPPORTED_LANGUAGES.md
SUPPORTED_STYLES.md		SUPPORTED_STYLES.md
astro.config.ts		astro.config.ts
bun.lockb		bun.lockb
package.json		package.json
playwright.config.ts		playwright.config.ts
tsconfig.json		tsconfig.json

License

metonym/svelte-highlight

Folders and files

Latest commit

History

Repository files navigation

svelte-highlight

Documentation

Installation

Basic Usage

Styling

Injected Styles

CSS StyleSheet

Linking from a CDN

Svelte Syntax Highlighting

Auto-highlighting

Line Numbers

Hidden Border

Wrapped Lines

Custom Starting Line Number

Highlighted Lines

Custom Styles

Language Targeting

Language Tags

Custom Language

Custom Plugin

Code-splitting

Component API

Highlight

Props

Dispatched Events

LineNumbers

Props

HighlightSvelte

Props

Dispatched Events

HighlightAuto

Props

Dispatched Events

Supported Languages

Supported Styles

Examples

Changelog

License

About

Topics

Resources

License

Stars

Watchers

Forks

Releases 54

Contributors 5

Languages

`Highlight`

`LineNumbers`

`HighlightSvelte`

`HighlightAuto`