Asynchronous Function Queue

gistfile1.js

var function_queue = [
  funcA,
  funcB,
  funcC,
  funcD
];
function doNextAction() {
  if (function_queue.length) {
     var next_function_call = function_queue.shift();
     next_function_call();
  }
}
function doProcess() {
  // do something.
  doNextAction();
}
function funcA() {
   doNextAction();
}
function funcB() {
 if (value is not null) {
    doNextAction();
    return;
 }
 // Result is null do something else.
 function_queue.unshift(funcD);
}
function funcC() {
 doNextAction();
}
function funcD() {
  // Done
}