callbackvflow.js

 'use strict';

(function () {
  var myfile;

  function readFileCallback(err, val) {
    if (err) throw err;
    
    myfile=val;

    console.log('in callback : ' + myfile);
  }      

  function callbackMaker(callback) {
    return function(err, vall) {
      readFileCallback(err, val);
      callback();
    } 
  }
  
  (require('fs')).readFile('betazoid.html',
                           callbackMaker(function () { console.log('post callback : ' + myfile); }));
}())