Code snippet that can wrap any function and give it the ability to run a callback

callbackWrapper.js

var callbackCurrier = function(obj, funcName) {
  var originalFunction = obj[funcName];
  var callbackFunc = function() {
    var args = Array.prototype.slice.call(arguments, 0);
    var callback = args.pop();
    var returnValue = originalFunction.apply(obj, args);
    if (callback) {
      callback(returnValue);
    }
  };
  obj[funcName] = callbackFunc;
};

example.js

var localStorageInterface = {
 getQuestion: function(questionId) {
  return localStorage.getItem('q' + questionId);
 },
 setQuestion: function(questionId, value) {
  localStorage.setItem('q' + questionId, value);
 }
}

// This could just as easily be a loop over an object's own properties,
// with a check that they are functions. Could also loop over an array
// of strings containing the function names that should return callbacks.
// Useful for enforcing an event-driven programming model on synchronous code.
callbackCurrier(localStorageInterface, 'getQuestion');
callbackCurrier(localStorageInterface, 'setQuestion');

localStorageInterface.setQuestion("status", "true", function() {
 localStorageInterface.getQuestion("status", function(data) {
  console.log(data);
 });
});