Elsewhere uses a simple logging system that writes to Node’s console. You can replace the logger with your own, for example, to store warnings and errors in a database or log file. To add your own custom logger, all you need to do is provide an object with the following interface:

{
  info:  function (message) { /* code to pass on message */ },
  log:   function (message) { /* code to pass on message */ },
  warn:  function (message) { /* code to pass on message */ },
  error: function (message) { /* code to pass on message */ }
}

You must then add this object to the logger property of the options object passed into the graph() method.