Pub/Sub, which means Publish-Subscribe, uses a more structured approach. Instead of depending on DOM components, it uses a central message bus, similar to an events message board. Here is the summary:

- Publishers: These are the event announcers who broadcast messages (events) via the messaging bus.
- Subscribers: These are the visitors who registered to receive specific announcements (events). When a relevant interaction comes, subscribers get notified and can take action.

Problem: Implement a simple version of Promise:

The Promise object is an asynchronous programming solution for handling asynchronous events. Promise objects can represent the status of an asynchronous operation, including:

- pending
- fulfilled
- rejected

Analysis:

🌶The MyPromise class is a custom Promise class whose constructor accepts an executor function as a parameter.
🌽The executor function in the constructor will be executed immediately and accepts two parameters, resolve and reject, which are used to modify the state of the Promise.
🍞The resolve method is used to modify the Promise’s status from “pending” to “fulfilled” and pass the value to subsequent handlers.
🥚The reject method is used to modify the Promise’s status from “pending” to “rejected” and pass the reason to the subsequent handler.
🍳The then method is used to register a callback function to be executed when the Promise is completed or rejected. It accepts two parameters: onFulfilled and onRejected, which are called when the Promise is completed or rejected respectively.
🥩The then method returns a new MyPromise instance to support chained calls. If onFulfilled or onRejected returns a value, it will be used as the resolved value for the next MyPromise instance.
🍔The catch method is the shorthand form of then(null, onRejected).
🍕The isFulfilled method is used to check whether the Promise is in the fulfilled state.
🌮The isRejected method is used to check whether the Promise is in the rejected state.