A powerful library for creating HTML sandboxes that support multiple dynamic files without network requests.
The magic-sandbox library allows you to combine multiple HTML, CSS, JavaScript, and data files into a single HTML document that works in any modern browser. It intelligently intercepts network requests to provide a seamless experience for code demonstrations, educational tools, and interactive editors.
Originally extracted from the Blockbuilder Project created by Ian Johnson and described in the Medium post Architecting a Sandbox.
- File Bundling: Combines multiple files into a single HTML document
- Request Interception: Intercepts XMLHttpRequest and fetch calls to load files without network requests
- Automatic Processing: Inlines JavaScript and CSS files referenced in HTML
- Protocol Fix: Converts protocol-less URLs (//example.com) to HTTPS
- Multiple File Types: Supports HTML, CSS, JavaScript, XML, CSV, and other file formats
npm install magic-sandboximport { magicSandbox, FileCollection } from "magic-sandbox";
// Define your files collection
const files: FileCollection = {
"index.html": `<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="styles.css">
</head>
<body>
<h1>Hello, World!</h1>
<script src="script.js"></script>
</body>
</html>`,
"styles.css": "h1 { color: blue; }",
"script.js": 'console.log("Hello from JavaScript!");',
"data.json": '{ "message": "This is data that can be fetched" }',
};
// Generate the HTML
const html = magicSandbox(files);
// Use in an iframe
document.getElementById("sandbox").setAttribute("srcdoc", html);magic-sandbox works by:
- Starting with your
index.htmlfile as a template - Inlining referenced JavaScript and CSS files when possible
- Injecting a script that intercepts XMLHttpRequest and fetch calls
- Encoding the contents of other files for access by the interceptor
- Fixing protocol-less URLs to use HTTPS
The result is a single HTML document that can reference and load multiple files without making any network requests.
import { magicSandbox, FileCollection } from "magic-sandbox";
// When files are updated in your editor
function updatePreview(files: FileCollection) {
const iframe = document.getElementById("preview");
const html = magicSandbox(files);
iframe.setAttribute("srcdoc", html);
}
// Example editor setup
const editor = setupCodeEditor(); // Your editor initialization
editor.onChange((files: FileCollection) => {
updatePreview(files);
});- Code Editors: Create live-preview code editors like CodePen or JSFiddle
- Educational Platforms: Build interactive coding exercises for students
- Demos & Examples: Showcase code examples with multiple files
- Documentation: Provide runnable code samples in documentation
Works in all modern browsers that support:
- iframes with the srcdoc attribute
- Fetch API
- XMLHttpRequest
- ES6 features
Contributions are welcome! Please feel free to submit a Pull Request.
MIT