a solution to implementing chaining http://www.thatjsdude.com/interview/js2.html

chain.js

function exec(fn){
  var doneCallback, failCallback, fnCallback,  fnEnded=false, _error, _data;
  
  exec.done = function(cb){
    doneCallback = cb;
    if(fnEnded && !_error){
      cb(_data); 
    }
    return exec;
  };
  
  exec.fail = function(cb){
    failCallback = cb;
    if(fnEnded &&_error){
      cb(_error); 
    }
    return exec;
  };
  
  fnCallback = function(error, data){
   _error = error;
    _data= data;
   if(failCallback && error){
     failCallback(error);
   }else if(doneCallback){
     doneCallback(data);
    }
    fnEnded=true;
  };
  
  fnStarted=true;
  fn(fnCallback);
  return exec;
}

function slow(callback) {
    setTimeout(function(){
        if (Math.random() > 0.5) {
            return callback("Error 417",null)
        }
        callback(null, {id:123})
    },500);
}

exec(slow).done(function(data){
    console.log(data);
}).fail(function(err){
    console.log("Error: " + err);
});