code: function(sourceFileName, code) {
  
      // If we're processing a block of code,
      // let's try to find a class name in the block to specify the sourceFileName
  
      var re = /class\s?([^\s]+)(\s?{|\s.*)|\s([^\s]+)\s?=\s?class/;
      var m = re.exec(code);
  
      return (sourceFileName || "") + (m && m[1] || nonce());
  }
docs: When concatenating multiple source map, each one need to have a specific source name,
  otherwize it will the last source will erase the previous ones.
  @param   {String} sourceFileName source file name original from options
  @param   {String} code           code associated
  @returns {String} a generated source file name unique form each codes