bluebird.promisify

promisify.js

Promise.promisify = function (fnThatTakesCallbacks) {

  return function () {
  
    var args = [].slice.call(arguments);
   
    return new Promise(function (resolve, reject) {
     
      fnThatTakesCallbacks.apply(this, args.concat(function (err) {
        
        if (err) return reject(err);
        
        var restOfArgs = [].slice.call(arguments, 1);
        
        if (restOfArgs.length < 2) {
          resolve(restOfArgs[0]);
        } else {
          resolve(restOfArgs);
        }
        
      }));
     
    });
  
  };

};