unrealDocRedirector.js

var forceVersion = '5.3';
var apiVersionRegex = /docs\.unrealengine\.com\/(?<apiVersion>\d+\.\d+)\/(?<languageTag>[0-9A-Za-z\-]+)\/(?<docPath>.*)$/;
var url = document.location.href;
var match = apiVersionRegex.exec(url);
var isVersionForced = typeof forceVersion !== 'undefined' && !isNaN(parseFloat(forceVersion));
if (match !== null) {
  var apiVersion = match.groups['apiVersion'];
  var languageTag = match.groups['languageTag'];
  var docPath = match.groups['docPath'];
  if (apiVersion !== undefined && languageTag !== undefined && docPath !== undefined) {
    var forceMajorVersion;
    var redirectUrl;
    if (isVersionForced) {
      forceMajorVersion = parseInt(forceVersion.split('.')[0]);
      if (forceMajorVersion < 5) {
        redirectUrl = `https://docs.unrealengine.com/${forceVersion}/${languageTag}/${docPath}`;
      } else {
        redirectUrl = `https://dev.epicgames.com/documentation/${languageTag}/unreal-engine/${docPath}?application_version=${forceVersion}`;
      }
    } else {
      redirectUrl = `https://dev.epicgames.com/documentation/${languageTag}/unreal-engine/${docPath}`;
    }
    window.location.replace(redirectUrl);
  }
}