Automatically Add $_GET Url Params from current request to all same-domain links on the page, that are part of a whitelist. HTML & JS code is exactly the same, simply copy-paste for non-teechies.

example.html

<script type="text/javascript">
  // The URL Params you want to whitelist, it will apply them on all links on the same domain.
  function rl_whitelisted_url_params() {
    return [ 'example-url-param', 'example-url-param-2', 'example-url-param-3' ];
  }

  function rl_get_url_param(parameterName) {
    var result = null,
        tmp    = [],
        items  = location.search.substr(1).split("&");

    for (var index = 0; index < items.length; index++) {
      tmp = items[index].split("=");
      if (tmp[0] === parameterName) result = decodeURIComponent(tmp[1]);
    }

    return result;
  }

  function rl_set_url_param(url, param, value) {
    param = encodeURIComponent(param);
    var r = "([&?]|&amp;)" + param + "\\b(?:=(?:[^&#]*))*";
    var a = document.createElement('a');
    var regex = new RegExp(r);
    var str = param + (value ? "=" + encodeURIComponent(value) : "");
    a.href = url;
    var q = a.search.replace(regex, "$1"+str);
    if (q === a.search) {
      a.search += (a.search ? "&" : "") + str;
    } else {
      a.search = q;
    }
    return a.href;
  }

  document.addEventListener('DOMContentLoaded', function () {
    var rl_url_params_full = rl_whitelisted_url_params(),
        rl_url_params = {},
        rl_links = document.getElementsByTagName('a'),
        rl_i = 0,
        rl_domain = window.location.protocol + '//' + window.location.host;

    for( rl_i = 0; rl_i < rl_url_params_full.length; rl_i++ ) {
      var param = rl_get_url_param( rl_url_params_full[rl_i] );

      if( param === null )
        continue;

      rl_url_params[ rl_url_params_full[rl_i] ] = param;
    }

    // No URL Params are actually provided
    if( Object.keys( rl_url_params ).length === 0 )
      return;


    for( rl_i = 0; rl_i < rl_links.length; rl_i++) {
      if( rl_links[rl_i].href.indexOf( rl_domain ) !== 0 )
        continue;

      var href = rl_links[rl_i].href;

      Object.keys( rl_url_params ).map(function(objectKey, index) {
        href = rl_set_url_param( href, objectKey, rl_url_params[objectKey] );
      });

      rl_links[rl_i].href = href;
    }
  });
</script>

example.js

// The URL Params you want to whitelist, it will apply them on all links on the same domain.
function rl_whitelisted_url_params() {
  return [ 'example-url-param', 'example-url-param-2', 'example-url-param-3' ];
}

function rl_get_url_param(parameterName) {
  var result = null,
      tmp    = [],
      items  = location.search.substr(1).split("&");

  for (var index = 0; index < items.length; index++) {
    tmp = items[index].split("=");
    if (tmp[0] === parameterName) result = decodeURIComponent(tmp[1]);
  }

  return result;
}

function rl_set_url_param(url, param, value) {
  param = encodeURIComponent(param);
  var r = "([&?]|&amp;)" + param + "\\b(?:=(?:[^&#]*))*";
  var a = document.createElement('a');
  var regex = new RegExp(r);
  var str = param + (value ? "=" + encodeURIComponent(value) : "");
  a.href = url;
  var q = a.search.replace(regex, "$1"+str);
  if (q === a.search) {
    a.search += (a.search ? "&" : "") + str;
  } else {
    a.search = q;
  }
  return a.href;
}

document.addEventListener('DOMContentLoaded', function () {
  var rl_url_params_full = rl_whitelisted_url_params(),
      rl_url_params = {},
      rl_links = document.getElementsByTagName('a'),
      rl_i = 0,
      rl_domain = window.location.protocol + '//' + window.location.host;

  for( rl_i = 0; rl_i < rl_url_params_full.length; rl_i++ ) {
    var param = rl_get_url_param( rl_url_params_full[rl_i] );

    if( param === null )
      continue;

    rl_url_params[ rl_url_params_full[rl_i] ] = param;
  }

  // No URL Params are actually provided
  if( Object.keys( rl_url_params ).length === 0 )
    return;


  for( rl_i = 0; rl_i < rl_links.length; rl_i++) {
    if( rl_links[rl_i].href.indexOf( rl_domain ) !== 0 )
      continue;

    var href = rl_links[rl_i].href;

    Object.keys( rl_url_params ).map(function(objectKey, index) {
      href = rl_set_url_param( href, objectKey, rl_url_params[objectKey] );
    });

    rl_links[rl_i].href = href;
  }
});