0_es5.js

var Constructor = function() {
  this.promise = myPromiseLib();
  this.onEventCallback = function(e) {
    return this.promise.resolve(e.name);
  }.bind(this);
  return this;
}

var item = new Constructor();
item.promise.then(function(result) {
  return result.name;
}).then(function(resultName) {
  return resultName.toUppercase();
})

1_es2015.js

var Constructor = function() {
  this.promise = myPromiseLib();
  this.onEventCallback = ({name}) => {
    return this.promise.resolve(name);
  };
  return this;
}

var item = new Constructor();
item.promise
  .then(result => result.name)
  .then(resultName => resultName.toUppercase());