async.js

function someAsyncThing(x) {
  return new Promise(function(resolve, reject) {
    // this will throw, x does not exist
    if (x > 10) {
      resolve(x);
    } else {
      reject(x);
    }
  });
};

someAsyncThing(343)
  .then(function(res) {
    console.log('everything is great is ', res);
  })
  .catch(function(error) {
    console.log('oh no', error);
  });