The observer pattern (also known as the publish-subscribe pattern) is a behavioral design pattern that defines one-to-many dependencies between objects, so that when the state of an object changes, its dependent objects are notified and automatically updated.
Implementing the observer pattern in j**ascript can be broken down into the following steps:
Create a subject object to store observer objects and provide APIs for adding, deleting, and notifying observers. Create an observer object, which has an update method to receive notifications from the subject object and process it accordingly. Here's a simple example:
class subject Add observer addobserver(observer) Remove observer removeobserver(observer) Notify observer notifyobservers() Class observer update() received the notification`)const subject = new subject();const observer1 = new observer('observer 1');const observer2 = new observer('observer 2');subject.addobserver(observer1);subject.addobserver(observer2);subject.notifyobservers();// output:// observer 1 received the notification.// observer 2 received the notification.In this example, the subject is the subject object and the observer is the observer object. subject provides an interface for adding, deleting, and notifying observers, and observer has an update method to receive notifications from subject objects and handle them accordingly. When using it, we can add the observer object to the subject object by calling the subject's addobserver method. When the state of a subject object changes, we can call the notifyobservers method to notify all observer objects to update.
The above is just a simple example, and there are more details to consider in practical application.