CloudFront Functions vs Lambda@Edge.

In Simple Words:

• CloudFront Functions: Lightweight JavaScript running at 450+ Edge Locations in sub-milliseconds. No network access. Ideal for URL rewrites, redirecting, and header manipulation.
• Lambda@Edge: Full Node.js/Python running at Regional Edge Caches. Allows network calls, third-party API lookups, and server-side rendering at the edge.

// CloudFront Function: URL rewrite appending index.html for SPAs:
function handler(event) {
  var request = event.request;
  var uri = request.uri;
  if (uri.endsWith('/')) {
    request.uri += 'index.html';
  } else if (!uri.includes('.')) {
    request.uri = '/index.html';
  }
  return request;
}