nodejs error stack trace is obtuse

file-watcher.js

const fs = require('fs'),
      fileName = process.argv[2];

if (!fileName) {
    throw Error("need to specify file to watch!");
}

fs.watch(fileName, function() {
    console.log("file '"+ fileName + "' just changed");
});

console.log("now watching '"+ fileName + "' for changes");

stacktrace.txt

/Users/deepak/Code/ScratchPad/learning-node/filewatch.js:5
    throw Error("need to specify file to watch!");
    ^

Error: need to specify file to watch!
    at Error (native)
    at Object.<anonymous> (/Users/deepak/Code/ScratchPad/learning-node/filewatch.js:5:11) # why Object.<anonymous> ?
    at Module._compile (module.js:398:26)
    at Object.Module._extensions..js (module.js:405:10)
    at Module.load (module.js:344:32)
    at Function.Module._load (module.js:301:12)
    at Function.Module.runMain (module.js:430:10)
    at startup (node.js:141:18)
    at node.js:1003:3