cloudfront lambda to redirect requests for folders to the index.html inside that folder

index.js

/*
redirect requests for folders to folders/index.html
*/

const resolveUrlEndingInSlashToIndexHtml = require('./resolve-url-ending-in-slash-to-index-html');

exports.handler = (event, context, callback) => {
  // Extract the request from the CloudFront event that is sent to Lambda@Edge
  const { request } = event.Records[0].cf;

  // Extract the URI from the request
  const olduri = request.uri;

  // Match any '/' that occurs at the end of a URI. Replace it with a default index
  const newuri = resolveUrlEndingInSlashToIndexHtml(olduri);

  // Log the URI as received by CloudFront and the new URI to be used to fetch from origin
  console.log(`Old URI: ${olduri}`);
  console.log(`New URI: ${newuri}`);

  // Replace the received URI with the URI that includes the index page
  request.uri = newuri;

  // Return to CloudFront
  return callback(null, request);
};

resolve-url-ending-in-slash-to-index-html.js

function resolveUrlEndingInSlashToIndexHtml(url) {
  // break url into parts
  const parts = url.split('/');
  console.log(url, parts);
  const lastPart = parts.pop();
  if (lastPart === '') {
    parts.push('index.html');
    return parts.join('/')
  }
  if (lastPart.indexOf('.') === -1) {
    parts.push(lastPart)
    parts.push('index.html');
    return parts.join('/');
  }
  return url;
  // return url.replace(/^.*\/([^\/\.]+)\/?$/, '\/$1\/index.html')
}

module.exports = resolveUrlEndingInSlashToIndexHtml;

resolve-url-ending-in-slash-to-index-html.test.js

const resolve = require('./resolve-url-ending-in-slash-to-index-html');

test('urls ending without an extension get /index.html appended', () => {
  expect(resolve('/')).toBe('/index.html');
  expect(resolve('/alice')).toBe('/alice/index.html');
  expect(resolve('/person/alice')).toBe('/person/alice/index.html');
  expect(resolve('/share-your-story')).toBe('/share-your-story/index.html');
});
test('urls ending with trailing slashes get index.html appended', () => {
  expect(resolve('/person/')).toBe('/person/index.html');
  expect(resolve('/person/alice/')).toBe('/person/alice/index.html');
  expect(resolve('/share-your-story/')).toBe('/share-your-story/index.html');
});
test('urls ending with extensions are untouched', () => {
  expect(resolve('/index.html')).toBe('/index.html');
  expect(resolve('/person/alice.html')).toBe('/person/alice.html');
  expect(resolve('/person/alice/story.html')).toBe('/person/alice/story.html');
  expect(resolve('/share-your-story.html')).toBe('/share-your-story.html');
});