Lambda function for url rewriting: lambda@edge function

function.js

const appendToDirs = 'index.html';
const regexSuffixless = /\/[^/.]+$/; // e.g. "/some/page" but not "/", "/some/" or "/some.jpg"
const regexTrailingSlash = /.+\/$/; // e.g. "/some/" or "/some/page/" but not root "/"

exports.handler = (event, context, callback) => {
  const { request } = event.Records[0].cf;
  const { uri } = request;

  // Append ".html" to origin request
  if (uri.match(regexSuffixless)) {
    request.uri = uri + '/' + appendToDirs;
    callback(null, request);
    return;
  }

  // Append "index.html" to origin request
  if (uri.match(regexTrailingSlash)) {
    request.uri = uri + appendToDirs;
    callback(null, request);
    return;
  }

  // If nothing matches, return request unchanged
  callback(null, request);
};