/*
 * extract twitter tweet query parameter from a URI. see google analytics docs for more info.
 */
function extractParamFromUri(uri, paramName) {
  if (!uri) {
    return;
  }
  var uri = uri.split('#')[0];  // Remove anchor.
  var parts = uri.split('?');  // Check for query params.
  if (parts.length == 1) {
    return;
  }
  var query = decodeURI(parts[1]);

  // Find url param.
  paramName += '=';
  var params = query.split('&');
  for (var i = 0, param; param = params[i]; ++i) {
    if (param.indexOf(paramName) === 0) {
      return unescape(param.split('=')[1]);
    }
  }
}