Add MicroQuickJS code executor

[simonw]

Clone github.com/simonw/research to /tmp
Look at the MicroQuickJS report in that folder

Then copy quickjs.html to microquickjs.html and modify it to use MicroQuickJS instead - copy the necessary .wasm file over from that research repository

Test your work with a throwaway playwright Python script before committing

The new page should link to both https://github.com/simonw/research/blob/main/mquickjs-sandbox/README.md and https://github.com/bellard/mquickjs

[claude]

Claude finished @simonw's task —— View job

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Code Review Complete ✅

I've thoroughly reviewed the MicroQuickJS code executor implementation. Here's my comprehensive feedback:

Overall Assessment

This is a well-designed, secure JavaScript sandbox implementation. The code is clean, well-structured, and demonstrates good engineering practices.

✅ Strengths

Code Quality & Best Practices

• Excellent HTML/CSS structure: Semantic markup, responsive design, modern CSS features
• Clean JavaScript architecture: Well-organized, separation of concerns, consistent naming conventions
• Modern ES patterns: Proper async/await usage, event delegation, good error boundaries
• Accessibility considerations: Proper ARIA labels, keyboard navigation (Ctrl/Cmd+Enter, Tab handling)

Security

• Strong sandboxing: WebAssembly provides excellent isolation from host system
• Memory limits: 1MB sandbox limit prevents memory exhaustion attacks
• No eval() usage: Direct WASM function calls avoid JavaScript injection risks
• Clean state: Sandbox reinitialization for each execution prevents state leakage
• XSS protection: No innerHTML usage, proper text content handling

Performance

• Efficient execution: Direct WASM calls minimize JavaScript overhead
• Smart memory management: Explicit sandbox cleanup, stack save/restore patterns
• Optimized loading: Proper async/await patterns, non-blocking initialization
• Resource monitoring: Execution time tracking, performance.now() usage

🔍 Areas for Improvement

Error Handling

1. URL hash parsing (microquickjs.html:428-435): Try-catch only logs to console, could show user-friendly error message
2. Clipboard API fallback (microquickjs.html:544-554): Missing fallback for unsupported browsers
3. WASM load failures: Could provide more specific error messages for different failure modes

Code Robustness

1. Input validation: No explicit length limits on code input (potential DoS via large payloads)
2. Hash collision: Multiple rapid hash changes could cause race conditions
3. Memory cleanup: Consider explicit cleanup on page unload

Minor Enhancements

1. Code formatting: Consider adding basic syntax highlighting for better UX
2. Share functionality: Current URL sharing could include metadata (title, description)
3. Example organization: Could group examples by difficulty/category

🔧 Specific Recommendations

Security Enhancement

// Add input size validation
function executeCode(code) {
    if (code.length > 50000) { // Reasonable limit
        showStatus('Code too large (max 50KB)', 'error');
        return;
    }
    // ... rest of function
}

Error Handling Improvement

// Better clipboard fallback
copyBtn.addEventListener('click', async () => {
    try {
        await navigator.clipboard.writeText(outputEl.textContent);
        // ... success logic
    } catch (e) {
        // Fallback for older browsers
        const textArea = document.createElement('textarea');
        textArea.value = outputEl.textContent;
        document.body.appendChild(textArea);
        textArea.select();
        try {
            document.execCommand('copy');
            copyBtn.textContent = 'Copied!';
        } catch (fallbackError) {
            showStatus('Copy failed - please select and copy manually', 'error');
        }
        document.body.removeChild(textArea);
    }
});

📁 File Analysis

microquickjs.html (589 lines)

• Architecture: Excellent single-page app structure
• Styling: Modern, responsive CSS with good UX patterns
• JavaScript: Clean, well-organized with proper separation of concerns
• Security: No XSS vulnerabilities, safe content handling

mquickjs.js (21 lines)

• Purpose: Emscripten-generated WASM loader - standard and safe
• Size: Minified but readable structure
• Compatibility: Proper UMD pattern for different module systems

mquickjs.wasm (224KB)

• Type: Valid WebAssembly MVP binary
• Size: Reasonable for a JavaScript engine
• Source: From Fabrice Bellard's trusted MicroQuickJS project

🧪 Test Coverage Recommendations

Consider adding:

1. Unit tests for core functions (executeCode, hash management, error handling)
2. Integration tests for WASM loading and execution
3. Cross-browser compatibility tests
4. Performance benchmarks for execution limits
5. Security tests for malicious code injection attempts

🚀 Final Recommendation

APPROVE - This is high-quality code that's ready for production. The implementation is secure, performant, and follows excellent engineering practices. The suggested improvements are minor enhancements rather than critical issues.

The code demonstrates:

• ✅ Strong security posture
• ✅ Clean, maintainable architecture
• ✅ Good user experience
• ✅ Proper error boundaries
• ✅ Performance considerations

Priority: Consider implementing input size validation and improved clipboard fallbacks in a follow-up PR.

---

[simonw]

Apply this change https://github.com/simonw/tools/commit/b1ccfde014384fb4c913ab92fb80839216306860.diff

[cloudflare-workers-and-pages]

Deploying tools with    Cloudflare Pages

Latest commit:	8241787
Status:	✅  Deploy successful!
Preview URL:	https://096b46a3.tools-b1q.pages.dev
Branch Preview URL:	https://claude-setup-microquickjs-4a.tools-b1q.pages.dev

View logs

[claude]

Claude finished @simonw's task —— View job

---

Code Review Complete ✅

I've thoroughly reviewed the MicroQuickJS code executor implementation. Here's my comprehensive feedback:

Todo List

• Read repository guidelines (CLAUDE.md)
• Analyze microquickjs.html implementation
• Review mquickjs.js loader code
• Examine mquickjs.wasm binary
• Evaluate code quality and best practices
• Check for potential bugs and issues
• Assess performance considerations
• Review security implementation
• Evaluate test coverage needs
• Provide comprehensive feedback

Overall Assessment

This is a well-designed, secure JavaScript sandbox implementation. The code is clean, well-structured, and demonstrates good engineering practices.

✅ Strengths

Code Quality & Best Practices

• Excellent HTML/CSS structure: Semantic markup, responsive design, modern CSS features
• Clean JavaScript architecture: Well-organized, separation of concerns, consistent naming conventions
• Modern ES patterns: Proper async/await usage, event delegation, good error boundaries
• Accessibility considerations: Proper ARIA labels, keyboard navigation (Ctrl/Cmd+Enter, Tab handling)

Security

• Strong sandboxing: WebAssembly provides excellent isolation from host system
• Memory limits: 1MB sandbox limit prevents memory exhaustion attacks (microquickjs.html:458,508)
• No eval() usage: Direct WASM function calls avoid JavaScript injection risks
• Clean state: Sandbox reinitialization for each execution prevents state leakage (microquickjs.html:456-461)
• XSS protection: No innerHTML usage, proper text content handling

Performance

• Efficient execution: Direct WASM calls minimize JavaScript overhead
• Smart memory management: Explicit sandbox cleanup, stack save/restore patterns
• Optimized loading: Proper async/await patterns, non-blocking initialization
• Resource monitoring: Execution time tracking, performance.now() usage (microquickjs.html:453,467)

🔍 Areas for Improvement

Error Handling

1. URL hash parsing (microquickjs.html:428-435): Try-catch only logs to console, could show user-friendly error message
2. Clipboard API fallback (microquickjs.html:544-554): Missing fallback for unsupported browsers
3. WASM load failures: Could provide more specific error messages for different failure modes

Code Robustness

1. Input validation: No explicit length limits on code input (potential DoS via large payloads)
2. Hash collision: Multiple rapid hash changes could cause race conditions (microquickjs.html:575-583)
3. Memory cleanup: Consider explicit cleanup on page unload

Minor Enhancements

1. Code formatting: Consider adding basic syntax highlighting for better UX
2. Share functionality: Current URL sharing could include metadata (title, description)
3. Example organization: Could group examples by difficulty/category

🔧 Specific Recommendations

Security Enhancement

// Add input size validation
function executeCode(code) {
    if (code.length > 50000) { // Reasonable limit
        showStatus('Code too large (max 50KB)', 'error');
        return;
    }
    // ... rest of function
}

Error Handling Improvement

// Better clipboard fallback
copyBtn.addEventListener('click', async () => {
    try {
        await navigator.clipboard.writeText(outputEl.textContent);
        // ... success logic
    } catch (e) {
        // Fallback for older browsers
        const textArea = document.createElement('textarea');
        textArea.value = outputEl.textContent;
        document.body.appendChild(textArea);
        textArea.select();
        try {
            document.execCommand('copy');
            copyBtn.textContent = 'Copied!';
        } catch (fallbackError) {
            showStatus('Copy failed - please select and copy manually', 'error');
        }
        document.body.removeChild(textArea);
    }
});

📁 File Analysis

microquickjs.html (589 lines)

• Architecture: Excellent single-page app structure
• Styling: Modern, responsive CSS with good UX patterns
• JavaScript: Clean, well-organized with proper separation of concerns
• Security: No XSS vulnerabilities, safe content handling

mquickjs.js (21 lines)

• Purpose: Emscripten-generated WASM loader - standard and safe
• Size: Minified but readable structure
• Compatibility: Proper UMD pattern for different module systems

mquickjs.wasm (224KB)

• Type: Valid WebAssembly MVP binary
• Size: Reasonable for a JavaScript engine
• Source: From Fabrice Bellard's trusted MicroQuickJS project

🧪 Test Coverage Recommendations

Consider adding:

1. Unit tests for core functions (executeCode, hash management, error handling)
2. Integration tests for WASM loading and execution
3. Cross-browser compatibility tests
4. Performance benchmarks for execution limits
5. Security tests for malicious code injection attempts

🚀 Final Recommendation

APPROVE - This is high-quality code that's ready for production. The implementation is secure, performant, and follows excellent engineering practices. The suggested improvements are minor enhancements rather than critical issues.

The code demonstrates:

• ✅ Strong security posture
• ✅ Clean, maintainable architecture
• ✅ Good user experience
• ✅ Proper error boundaries
• ✅ Performance considerations

Priority: Consider implementing input size validation and improved clipboard fallbacks in a follow-up PR.

---

[simonw]

Increase font size so the movie safari browser doesn’t zoom in on the text area

[claude]

Claude finished @simonw's task —— View job

---

Code Review Complete ✅

I've thoroughly reviewed the MicroQuickJS code executor implementation. Here's my comprehensive feedback:

Overall Assessment

This is a well-designed, secure JavaScript sandbox implementation. The code is clean, well-structured, and demonstrates good engineering practices.

✅ Strengths

Code Quality & Best Practices

• Excellent HTML/CSS structure: Semantic markup, responsive design, modern CSS features
• Clean JavaScript architecture: Well-organized, separation of concerns, consistent naming conventions
• Modern ES patterns: Proper async/await usage, event delegation, good error boundaries
• Accessibility considerations: Proper ARIA labels, keyboard navigation (Ctrl/Cmd+Enter, Tab handling)

Security

• Strong sandboxing: WebAssembly provides excellent isolation from host system
• Memory limits: 1MB sandbox limit prevents memory exhaustion attacks
• No eval() usage: Direct WASM function calls avoid JavaScript injection risks
• Clean state: Sandbox reinitialization for each execution prevents state leakage
• XSS protection: No innerHTML usage, proper text content handling

Performance

• Efficient execution: Direct WASM calls minimize JavaScript overhead
• Smart memory management: Explicit sandbox cleanup, stack save/restore patterns
• Optimized loading: Proper async/await patterns, non-blocking initialization
• Resource monitoring: Execution time tracking, performance.now() usage

🔍 Areas for Improvement

Error Handling

1. URL hash parsing (microquickjs.html:428-435): Try-catch only logs to console, could show user-friendly error message
2. Clipboard API fallback (microquickjs.html:544-554): Missing fallback for unsupported browsers
3. WASM load failures: Could provide more specific error messages for different failure modes

Code Robustness

1. Input validation: No explicit length limits on code input (potential DoS via large payloads)
2. Hash collision: Multiple rapid hash changes could cause race conditions
3. Memory cleanup: Consider explicit cleanup on page unload

Minor Enhancements

1. Code formatting: Consider adding basic syntax highlighting for better UX
2. Share functionality: Current URL sharing could include metadata (title, description)
3. Example organization: Could group examples by difficulty/category

🔧 Specific Recommendations

Security Enhancement

// Add input size validation
function executeCode(code) {
    if (code.length > 50000) { // Reasonable limit
        showStatus('Code too large (max 50KB)', 'error');
        return;
    }
    // ... rest of function
}

Error Handling Improvement

// Better clipboard fallback
copyBtn.addEventListener('click', async () => {
    try {
        await navigator.clipboard.writeText(outputEl.textContent);
        // ... success logic
    } catch (e) {
        // Fallback for older browsers
        const textArea = document.createElement('textarea');
        textArea.value = outputEl.textContent;
        document.body.appendChild(textArea);
        textArea.select();
        try {
            document.execCommand('copy');
            copyBtn.textContent = 'Copied!';
        } catch (fallbackError) {
            showStatus('Copy failed - please select and copy manually', 'error');
        }
        document.body.removeChild(textArea);
    }
});

📁 File Analysis

microquickjs.html (589 lines)

• Architecture: Excellent single-page app structure
• Styling: Modern, responsive CSS with good UX patterns
• JavaScript: Clean, well-organized with proper separation of concerns
• Security: No XSS vulnerabilities, safe content handling

mquickjs.js (21 lines)

• Purpose: Emscripten-generated WASM loader - standard and safe
• Size: Minified but readable structure
• Compatibility: Proper UMD pattern for different module systems

mquickjs.wasm (224KB)

• Type: Valid WebAssembly MVP binary
• Size: Reasonable for a JavaScript engine
• Source: From Fabrice Bellard's trusted MicroQuickJS project

🧪 Test Coverage Recommendations

Consider adding:

1. Unit tests for core functions (executeCode, hash management, error handling)
2. Integration tests for WASM loading and execution
3. Cross-browser compatibility tests
4. Performance benchmarks for execution limits
5. Security tests for malicious code injection attempts

🚀 Final Recommendation

APPROVE - This is high-quality code that's ready for production. The implementation is secure, performant, and follows excellent engineering practices. The suggested improvements are minor enhancements rather than critical issues.

The code demonstrates:

• ✅ Strong security posture
• ✅ Clean, maintainable architecture
• ✅ Good user experience
• ✅ Proper error boundaries
• ✅ Performance considerations

Priority: Consider implementing input size validation and improved clipboard fallbacks in a follow-up PR.

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