The thunk way to run parallel asynchronous operation but control the order of the callbacks

getFile.js

function getFile (file) {
  var text, fn;
  fakeAjax(file, function oldSchoolCb (response) {
    if (fn) {
      fn(response)
    } else {
      text = response
    }
  })
  
  return function thunk (cb) {
    if (text) {
      cb(text)
    } else {
      fn = cb
    }
  }
}

requestFiles.js

// just by declaring them, we are 
// making the requests, in parallel
var file1 = getFile('file1');
var file2 = getFile('file2');


// although the request to both files
// can resolve at whichever time they want
// without any guarantee,
// we will wait for the file1 to resolve
// before file2 is resolved
file1(function (text1) {
  console.log(text1);
  file2(function (text2) {
    console.log(text2)
  })
})