text: var idGen = require( './id-gen' );
  var getFnId = idGen.create( 'fn' );
  
  module.exports = function getIdOfCallback( callback ) {
    var eleId = callback.xFId;
    if ( !eleId ) {
      eleId = getFnId();
      callback.xFId = eleId;
    }
    return eleId;
  };
  