Convert tOSU-callback-hell.js to promise for article on http://theopensourceu.org/concepts-to-implementations-promise/

tOSU-promises.js

//
// require statements omitted for readability and brevity.
var readFile = Promise.promisify(require("fs").readFile); //See http://bluebirdjs.com/docs/api/promise.promisify.html

function processData( startData ) {
  //Return a promise which impl will use "then" to implement what was "cbResult"
  return new Promise( function(resolve) {
    //
    // Do something with startingData and ultimatly set result to finalizedResult.
    // ...
    var finalizedResult = startingData;
    return finalizedResult; //Returning something makes it available in chained 'then' statements.
  } );
}

function parentMethod() {
  readFile('/my/made/up/file.txt')
    .then(function callback1(data) {    //Note that (data) => {} is a newer way of defining a function in JS. 
      return processData( data );       //Not available everywhere yet though. Equiv. to function(data) {}
    })
    .then(function callback2(results) {
      return sendResultsToServer(result);
    })
    .then(function callback3(response) {
      executionOrderIsClearer(); //as well as where each method starts and ends.
    })
    .catch(function(err) {
      // Handle errors from the readFile to callback3. 
      // Like wraping the above in a try/catch
    });
}