prerender lambda@edge

viewer-request.js

'use strict';

const customUserAgentHeaderName = 'x-is-bot';
exports.handler = (event, context, callback) => {
  const request = event.Records[0].cf.request;
  const headers = request.headers;

  const userAgent = headers['user-agent'][0].value;
  
  headers[customUserAgentHeaderName] = [{
    key: 'x-is-bot',
    value: checkIfBot(userAgent).toString()
  }]

  callback(null, request);
};

function checkIfBot(userAgent) {
  if (userAgent) {

    const botUserAgents = [
      'googlebot',
      'Yahoo! Slurp',
      'bingbot',
      'yandex',
      'baiduspider',
      'facebookexternalhit',
      'twitterbot',
      'rogerbot',
      'linkedinbot',
      'embedly',
      'quora link preview',
      'showyoubot',
      'outbrain',
      'pinterest/0.',
      'developers.google.com/+/web/snippet',
      'slackbot',
      'vkShare',
      'W3C_Validator',
      'redditbot',
      'Applebot',
      'WhatsApp',
      'flipboard',
      'tumblr',
      'bitlybot',
      'SkypeUriPreview',
      'nuzzel',
      'Discordbot',
      'Google Page Speed',
      'Qwantify',
      'pinterestbot',
      'Bitrix link preview',
      'XING-contenttabreceiver',
      'Chrome-Lighthouse'
    ];


    if (botUserAgents.some(function (botUserAgent) {
        return userAgent.toLowerCase().indexOf(botUserAgent) !== -1;
      })) {
      return true;
    }
    return false;
  }
  return false;
}