gistfile1.js

var myFuncWithPromise = function() {
  return new Promise(function(resolve, reject) {
    // if everything goes well then..
    if (everythingWentWell) return resolve('success!');
    // otherwise, reject it and send along an error
    return reject(new Error('wtf dude'));
  });
};

myFuncWithPromise()
.then(function(result) {
  console.log(result); // <-- would be 'success!'
}).catch(function(err) {
  console.log(err.message); // <-- would be 'wtf dude'
});