aws s3 api gateway cloudfront lambda@edge function which fixes subdirectory in static website hosting by redirecting "**/" to "**/index.html"

cloudfront-default-object.lambda.js

// BASIC

'use strict';
exports.handler = (event, context, callback) => {
  // Extract the request from the CloudFront event
  const {request} = event.Records[0].cf;

  // Extract the URI from the request
  const {uri} = request;

  // Return to CloudFront
  return callback(
    // No error
    null,
    // Modify a clone of the request object using spread operation
    {
      ...request,
      // Override uri, atch any '/' that occurs at the end of a URI. Replace it with a default index
      uri: uri.replace(/\/$/, '\/index.html'),
    }
  );
};

// WITH WWW AND LANGUAGE REDIRECT LOGIC

'use strict';
exports.handler = (event, context, callback) => {
  // Extract the request from the CloudFront event
  const {request} = event.Records[0].cf;

  // Extract the URI from the request
  const {origin, uri, headers} = request;

  // If domain has'www', redirect to base domain, without 'www'
  if ((/^www\./).test(((origin || {}).custom || {}).domainName)) {
    const fixedDomain = origin.custom.domainName.replace(/^www\./, '');

    return callback(
      // No error
      null,
      {
        status: '301',
        statusDescription: 'Moved Permanently',
        headers: {
          'location': [{
            key: 'Location',
            value: `https://${fixedDomain}${uri}`,
          }],
          'cache-control': [{
            key: 'Cache-Control',
            value: "max-age=3600"
          }],
        },
      },
    );
  }
  
  let response;
  
  if(request.uri == '/') {
    // for proper SEO, if request is for root, redirect to appropriate language
    response = {
      status: '301',
      statusDescription: 'Moved Permanently',
      headers: {
        'location': [{
          key: 'Location',
          value: '/en/',
        }],
        'cache-control': [{
          key: 'Cache-Control',
          value: "max-age=3600"
        }],
      },
    };

    if (typeof headers['accept-language'] !== 'undefined') {
      const supportedLanguages = (headers['accept-language'][0] || {}).value || '';

      if(supportedLanguages.startsWith('es')){
        response.headers.location[0].value = '/es/';
      }
    }
  } else {
    // Modify a clone of the request object using spread operation
    response = {
      ...request,
      // Override uri, atch any '/' that occurs at the end of a URI. Replace it with a default index
      uri: uri.replace(/\/$/, '\/index.html'),
    }
  }

  // Return to CloudFront
  return callback(
    // No error
    null,
    response,
  );
};

trust.relationships.json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": [
          "edgelambda.amazonaws.com",
          "lambda.amazonaws.com"
        ]
      },
      "Action": "sts:AssumeRole"
    }
  ]
}