Buy Button Broken on iPhone: Copilot Browser Bug

The problem

Our e-commerce client was losing 42% of mobile sales. iPhone users complained the buy button was completely unresponsive - they'd tap it repeatedly but nothing happened. No loading spinner, no error message, just dead silence. Analytics showed massive cart abandonment rates specifically on iOS Safari, costing them $18,000 in lost revenue per week.

How AI created this issue

The developer asked GitHub Copilot to "create a modern buy button with loading state". Copilot generated this code:

// Copilot-generated code
const BuyButton = () => {
  const [loading, setLoading] = useState(false);
  
  const handlePurchase = async (e) => {
    e.preventDefault();
    setLoading(true);
    
    // Using optional chaining and nullish coalescing
    const formData = e.target?.form?.data ?? {};
    
    // Modern async/await with AbortController
    const controller = new AbortController();
    const response = await fetch('/api/purchase', {
      signal: controller.signal,
      body: JSON.stringify(formData)
    });
    
    setLoading(false);
  };
  
  return (
    <button onClick={handlePurchase} className="buy-btn">
      {loading ? <Spinner /> : 'Buy Now'}
    </button>
  );
};

The issue? Copilot used cutting-edge JavaScript features that iOS Safari 14 (still used by 15% of iPhone users) doesn't support. The optional chaining (?.), nullish coalescing (??), and AbortController weren't polyfilled, causing the entire button handler to silently fail on older iOS devices.

The solution

1. Cross-browser testing setup: Implemented BrowserStack testing to catch iOS-specific issues before deployment
2. Fixed the JavaScript: Rewrote the button handler with broader compatibility:

   
   // Cross-browser compatible version
   const handlePurchase = async (e) => {
     e.preventDefault();
     setLoading(true);
     
     try {
       // Fallback for older browsers
       const form = e.target && e.target.form;
       const formData = form && form.data ? form.data : {};
       
       // Standard fetch without AbortController
       const response = await fetch('/api/purchase', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify(formData)
       });
       
       if (!response.ok) throw new Error('Purchase failed');
       
       // Success handling
       window.location.href = '/order-confirmation';
     } catch (error) {
       console.error('Purchase error:', error);
       alert('Purchase failed. Please try again.');
     } finally {
       setLoading(false);
     }
   };

3. Added polyfills: Implemented core-js polyfills for Promise and fetch support
4. Mobile-specific testing: Created a test suite specifically for iOS Safari 12-16
5. Error tracking: Added Sentry monitoring to catch any future mobile-specific failures

The results

Within 24 hours of deploying the fix:

• Mobile conversion rate jumped from 1.2% to 3.8% - matching desktop performance
• Recovered $18,000/week in lost mobile revenue
• Zero reported button failures across all iOS versions
• Page load time improved by 0.3s after removing unnecessary polyfills
• Customer support tickets dropped 78% as frustrated mobile users could finally purchase

The client learned a valuable lesson: AI-generated code often targets the latest browser features without considering the real-world device landscape. Now they test every feature on actual devices before deployment.