node helloworld_example.js

module.js:340
throw err;
Error: Cannot find module 'now'
   at Function.Module._resolveFilename (module.js:338:15)
   at Function.Module._load (module.js:280:25)
   at Module.require (module.js:362:17)
   at require (module.js:378:17)
   at Object.<anonymous> (/Users/toptierlabs/Desktop/node/helloworld_server.js:10:13)
   at Module._compile (module.js:449:26)
   at Object.Module._extensions..js (module.js:467:10)
   at Module.load (module.js:356:32)
   at Function.Module._load (module.js:312:12)
   at Module.runMain (module.js:492:10)