Wraps the execution of asynchronous operations, providing a promise object that can be used to subscribe to the various ways the operation may terminate.

When the operation completes successfully, call the Resolver's resolve() method, passing any relevant response data for subscribers. If the operation encounters an error or is unsuccessful in some way, call reject(), again passing any relevant data for subscribers.

The Resolver object should be shared only with the code resposible for resolving or rejecting it. Public access for the Resolver is through its promise, which is returned from the Resolver's promise property. While both Resolver and promise allow subscriptions to the Resolver's state changes, the promise may be exposed to non-controlling code. It is the preferable interface for adding subscriptions.

Subscribe to state changes in the Resolver with the promise's then(callback, errback) method. then() wraps the passed callbacks in a new Resolver and returns the corresponding promise, allowing chaining of asynchronous or synchronous operations. E.g. promise.then(someAsyncFunc).then(anotherAsyncFunc)