fn is not defined

[icewitch]

fn is not defined, if I have tried to modify fn to end, there is no output in the console. How to use the codes correctly?

D:\node\pool.js:3
superagent.get('http://google.com',fn)
^

ReferenceError: fn is not defined
at Object. (D:\node\pool.js:3:36)
at Module._compile (module.js:652:30)
at Object.Module._extensions..js (module.js:663:10)
at Module.load (module.js:565:32)
at tryModuleLoad (module.js:505:12)
at Function.Module._load (module.js:497:3)
at Function.Module.runMain (module.js:693:10)
at startup (bootstrap_node.js:188:16)
at bootstrap_node.js:609:3