Lambda@Edge to carry out redirects and apply default documents (index.html) to incoming requests

lambda.js

  var path = require('path');

  const redirects = {
    "/about-us": { to: "/about", statusCode: 301 },
    "/contact-us/head-office": { to: "/contact/head-office", statusCode: 302 },
  };

  exports.handler = async event => {
    const { request } = event.Records[0].cf;
    const normalisedUri = normalise(request.uri);
    const redirect = redirects[normalisedUri];
    if (redirect) {
      return redirectTo(redirect.to, redirect.statusCode);
    }
    if (!hasExtension(request.uri)) {
      request.uri = trimSlash(request.uri) + "/index.html";
    }
    return request;
  };

  const trimSlash = uri => hasTrailingSlash(uri) ? uri.slice(0, -1) : uri;
  const normalise = uri => trimSlash(uri).toLowerCase();
  const hasExtension = uri => path.extname(uri) !== '';
  const hasTrailingSlash = uri => uri.endsWith('/');

  const redirectTo = (to, statusCode) => ({
    status: statusCode.toString(),
    statusDescription: 'Found',
    headers: {
      location: [{
        key: 'Location',
        value: to,
      }],
    },
  });