Decorate Link with Query String

<script>
  (function() {
    // List of domains to decorate (without https or trailing slash)
    var domainsToDecorate = ['booker.com', 'somedomain.com'];

    // Value to be set as linker param
    var referrerDomain = 'ref-domain=' + document.location.hostname + '-praba-test';

    // Get all the links
    var links = document.querySelectorAll('a');

    // Filter the required domains
    for (var linkIndex = 0; linkIndex < links.length; linkIndex++) {
      for (var domainIndex = 0; domainIndex < domainsToDecorate.length; domainIndex++) {
        if (links[linkIndex].href.indexOf(domainsToDecorate[domainIndex]) > -1 && links[linkIndex].href.indexOf("#") === -1) {
          links[linkIndex].href = decorateUrl(links[linkIndex].href);
        }
      }
    }

    // decorates the URL with query params
    function decorateUrl(urlToDecorate) {
      urlToDecorate = (urlToDecorate.indexOf('?') === -1) ? urlToDecorate + '?' : urlToDecorate + '&';
      return urlToDecorate + '&' + referrerDomain;
    }

    // Append value as query parameter
    function getQueryParam(name) {
      if (name = (new RegExp('[?&]' + encodeURIComponent(name) + '=([^&]*)')).exec(window.location.search)) return decodeURIComponent(name[1]);
    }
  })();
</script>