CloudFront Function to rewrite uri in s3 backend (leave only the last path) & add index.html for static websites

cloudfront-function-rewrite.js

function handler(event) {
  var request = event.request;
	
  // Example: 
  // Input:  /app1/assets/test.jpg
  // Output: /assets/test.jpg
  request.uri = request.uri.replace(/^\/[^/]*\//, "/");
	
  // Check whether the URI is missing a file name.
  if (request.uri.endsWith('/')) {
    request.uri += 'index.html';
  }
	
  // Check whether the URI is missing a file extension.
  else if (!request.uri.includes('.')) {
    request.uri += '/index.html';
  }
	
  return request;
}