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How to handle Observable in Angular

Observables provide support for passing messages between parts of your application. They are used frequently in Angular and are a technique for event handling, asynchronous programming, and handling multiple values.
The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of state changes. This pattern is similar (but not identical) to the publish/subscribe design pattern.
Observables are declarative —that is, you define a function for publishing values, but it is not executed until a consumer subscribes to it. The subscribed consumer then receives notifications until the function completes, or until they unsubscribe.
An observable can deliver multiple values of any type —literals, messages, or events, depending on the context. The API for receiving values is the same whether the values are delivered synchronously or asynchronously. Because setup and teardown logic are both handled by the observable, your application code only needs to worry about subscribing to consume values, and when done, unsubscribing. Whether the stream was keystrokes, an HTTP response, or an interval timer, the interface for listening to values and stopping listening is the same.