Prism.js Complete Guide: Making Your Blog Code More Readable with Syntax Highlighting

What is Prism.js?

Prism.js is a lightweight, extensible syntax highlighting library. It makes code blocks on websites or blogs beautiful and significantly improves readability.

Why Prism.js?

🚀 Lightweight: Only about 2KB minified for fast loading
🎨 Beautiful Themes: Pre-built, gorgeous themes available
🔌 Plugin System: Extensible with various plugins
🛠️ Easy to Use: Works out of the box with simple setup
📦 200+ Languages: Supports most programming languages

Installation and Basic Usage

Install via npm

npm install prismjs

Use via CDN

<!-- CSS -->
<link href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/themes/prism.min.css" rel="stylesheet" />

<!-- JavaScript -->
CODE0

Basic Usage

<pre><code class="language-javascript">
function greet(name) {
    return `Hello, ${name}!`;
}

console.log(greet('World'));
</code></pre>

Prism.js automatically recognizes language-* classes and highlights the code accordingly.

Integrating Prism.js with Eleventy

Since Eleventy is a static site generator, you can highlight code at build time.

1. Install the Plugin

npm install @11ty/eleventy-plugin-syntaxhighlight

2. Add to Eleventy Configuration

Open your .eleventy.js file and configure it as follows:

const syntaxHighlight = require("@11ty/eleventy-plugin-syntaxhighlight");

module.exports = function(eleventyConfig) {
  // Add Prism.js plugin
  eleventyConfig.addPlugin(syntaxHighlight, {
    preAttributes: {
      class: ({ language }) => `language-${language}`
    }
  });
  
  // Copy Prism.js theme CSS
  eleventyConfig.addPassthroughCopy({
    "node_modules/prismjs/themes/prism-tomorrow.css": "css/prism-theme.css"
  });

  return {
    // ... other configurations
  };
};

3. Add CSS to Layout

Add this to the <head> section of src/_layouts/base.njk:

<link rel="stylesheet" href="/css/prism-theme.css">

4. Use in Markdown

Now you can write code blocks in markdown and they’ll be automatically highlighted:

```javascript
const data = {
  name: "Prism.js",
  version: "1.29.0"
};

console.log(JSON.stringify(data, null, 2));
```

Supported Languages

Prism.js supports over 200 languages:

Frontend: JavaScript, TypeScript, HTML, CSS, Sass, Less
Backend: Java, Python, PHP, Ruby, Go, Rust
Database: SQL, MongoDB
Tools: Bash, Git, YAML, JSON, Markdown
Others: C, C++, C#, Swift, Kotlin, and more

Specify languages using the language-* class:

<pre><code class="language-python">print("Hello, World!")</code></pre>
<pre><code class="language-java">System.out.println("Hello, World!");</code></pre>
<pre><code class="language-sql">SELECT * FROM users;</code></pre>

Theme Customization

Choose a Default Theme

Prism.js offers several themes:

prism.css - Default theme
prism-dark.css - Dark theme
prism-tomorrow.css - Tomorrow theme (recommended)
prism-okaidia.css - Okaidia theme
prism-twilight.css - Twilight theme

To change themes via CDN:

<!-- Default theme -->
<link href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/themes/prism.min.css" rel="stylesheet" />

<!-- Dark theme -->
<link href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/themes/prism-dark.min.css" rel="stylesheet" />

<!-- Tomorrow theme -->
<link href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/themes/prism-tomorrow.min.css" rel="stylesheet" />

Create a Custom Theme

You can create a custom theme by creating a CSS file:

/* custom-prism-theme.css */
code[class*="language-"],
pre[class*="language-"] {
  color: #f8f8f2;
  background: #272822;
  text-shadow: 0 1px rgba(0, 0, 0, 0.3);
  font-family: 'Fira Code', 'Consolas', monospace;
  font-size: 1em;
  text-align: left;
  white-space: pre;
  word-spacing: normal;
  word-break: normal;
  line-height: 1.5;
  tab-size: 4;
  hyphens: none;
}

.token.comment,
.token.prolog,
.token.doctype,
.token.cdata {
  color: #75715e;
}

.token.punctuation {
  color: #f8f8f2;
}

.token.property,
.token.tag,
.token.constant,
.token.symbol,
.token.deleted {
  color: #f92672;
}

.token.boolean,
.token.number {
  color: #ae81ff;
}

.token.selector,
.token.attr-name,
.token.string,
.token.char,
.token.builtin,
.token.inserted {
  color: #a6e22e;
}

.token.operator,
.token.entity,
.token.url,
.language-css .token.string,
.style .token.string,
.token.variable {
  color: #f8f8f2;
}

.token.atrule,
.token.attr-value,
.token.function,
.token.class-name {
  color: #e6db74;
}

.token.keyword {
  color: #66d9ef;
}

Useful Plugins

Prism.js has various useful plugins:

1. Line Numbers

npm install prismjs

import Prism from 'prismjs';
import 'prismjs/plugins/line-numbers/prism-line-numbers.css';
import 'prismjs/plugins/line-numbers/prism-line-numbers.js';

// Add class to HTML
// <pre class="line-numbers"><code class="language-javascript">...</code></pre>

2. Copy to Clipboard

CODE1

CODE2
<link href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/plugins/toolbar/prism-toolbar.min.css" rel="stylesheet" />

4. Show Language

CODE3

Practical Example: Applying to Eleventy Blog

Complete Configuration Example

.eleventy.js:

const syntaxHighlight = require("@11ty/eleventy-plugin-syntaxhighlight");

module.exports = function(eleventyConfig) {
  // Configure Prism.js plugin
  eleventyConfig.addPlugin(syntaxHighlight, {
    preAttributes: {
      class: ({ language }) => `language-${language}`,
      'data-line': ({ lineStart, lineEnd }) => 
        lineStart ? `${lineStart}${lineEnd ? `-${lineEnd}` : ''}` : undefined
    },
    codeAttributes: {
      'data-language': ({ language }) => language
    }
  });

  // Copy Prism.js theme
  eleventyConfig.addPassthroughCopy({
    "node_modules/prismjs/themes/prism-tomorrow.css": "css/prism-theme.css"
  });

  return {
    dir: {
      input: "src",
      output: "_site"
    }
  };
};

Adding Copy to Clipboard Feature

js/code-copy.js:

document.addEventListener('DOMContentLoaded', function() {
  const codeBlocks = document.querySelectorAll('pre code');
  
  codeBlocks.forEach(block => {
    const pre = block.parentElement;
    
    // Skip if copy button already exists
    if (pre.querySelector('.copy-button')) return;
    
    // Create copy button
    const button = document.createElement('button');
    button.className = 'copy-button';
    button.textContent = 'Copy';
    button.style.cssText = `
      position: absolute;
      top: 10px;
      right: 10px;
      padding: 5px 10px;
      background: #333;
      color: #fff;
      border: none;
      border-radius: 4px;
      cursor: pointer;
      font-size: 12px;
    `;
    
    // Add relative positioning to pre
    pre.style.position = 'relative';
    
    button.addEventListener('click', async () => {
      const text = block.textContent;
      await navigator.clipboard.writeText(text);
      button.textContent = 'Copied!';
      setTimeout(() => {
        button.textContent = 'Copy';
      }, 2000);
    });
    
    pre.appendChild(button);
  });
});

Performance Optimization

Load Only Required Languages

Loading all languages increases bundle size. Only load what you need:

import Prism from 'prismjs';

// Import only required languages
import 'prismjs/components/prism-javascript';
import 'prismjs/components/prism-typescript';
import 'prismjs/components/prism-python';
import 'prismjs/components/prism-java';

Prism.highlightAll();

Disable Auto Highlighting

To highlight only specific code blocks:

// Disable auto highlighting
Prism.plugins.autoloader.languages_path = 'https://cdn.jsdelivr.net/npm/prismjs@1.29.0/components/';

// Highlight only specific elements
const codeBlocks = document.querySelectorAll('.highlight');
codeBlocks.forEach(block => {
  Prism.highlightElement(block);
});

Conclusion

Prism.js is one of the best ways to add syntax highlighting to your blog or website. With simple configuration, you can create beautiful code blocks and have access to various customization options.

Using it with Eleventy allows code highlighting at build time, providing better performance and SEO benefits. Now try applying Prism.js to your blog!