How do edge computing runtimes like Cloudflare Workers enhance JavaScript application performance and global scalability?

export default {
  async fetch(request, env, ctx) {
    const url = new URL(request.url);
    
    // Geo-personalized response
    if (url.pathname === '/greet') {
      const country = request.cf.country;
      return new Response(`Hello from ${country}!`, {
        headers: { 'Cache-Control': 's-maxage=300' }
      });
    }
    
    // Proxy with transformation
    const upstream = await fetch('https://api.example.com' + url.pathname);
    const data = await upstream.json();
    data.region = request.cf.region;
    
    return Response.json(data);
  }
};