HttpClient.get() method called but its not subscribed can you explain all expect

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[sunilnetin]

When an HttpClient.get() method is not subscribed, nothing happens.
This behavior is a core concept of RxJS, the reactive programming library that Angular's HttpClient is built upon. The HttpClient's methods return "cold observables," which are lazy. This means the observable only starts executing its task—in this case, making an HTTP request—when it has a subscriber.

[sunilnetin]

Here is a full breakdown of the expectations and why this behavior is crucial for Angular applications.
Explanation of "cold observable"
The observable returned by HttpClient.get() is a cold observable. This means it acts as a blueprint or recipe for making an HTTP request.
Simply calling the .get() method does not trigger the request.
The work is only performed when an observer subscribes to the observable.
The subscription signals the observable to make the request and prepares to receive data.
Expectations when not subscribed
If this.http.get('/api/data') is called without a .subscribe() method, the following occurs:
No HTTP request is sent: The application does not send a request to the server, and there is no network activity.
No data is received: Since the request is not made, no server response is processed, and the component receives no data.
No errors are handled: If the HTTP request fails, the observable emits an error notification. Without a subscriber, there is no error handler to process the error.
No memory leak risk: Because no subscription is created, there is nothing to unsubscribe from. However, this is not beneficial, because the code doesn't function as intended.

[sunilnetin]

How it works when subscribed
When properly subscribed to the observable, the request executes. The subscription also defines what happens with the result.
// Call the get method and subscribe to the returned observable
this.http.get('/api/users').subscribe({
// 'next' is the handler for successful responses
next: (data) => {
// This code runs when data is received
this.users = data;
console.log('Data received:', data);
},
// 'error' is the handler for failed requests
error: (err) => {
// This code runs if the request fails
console.error('An error occurred:', err);
},
// 'complete' runs after the observable finishes
complete: () => {
console.log('The request is complete.');
}
});

Benefits of this design
This "lazy" observable pattern is an intentional and powerful feature of reactive programming.
Enables operators: This allows for chaining multiple RxJS operators (pipe, map, filter, etc.) to transform and manipulate the data stream before the request is made. The entire chain of operations is defined first, and the execution is deferred until you subscribe.
Manages side effects: Requiring a subscription to trigger the request explicitly states when a side effect (like an API call) should occur. This provides precise control over data fetching.
Supports multiple subscriptions: Subscribing multiple times to the same HttpClient observable triggers the request for each subscription. This is useful when different application parts need to trigger the same request independently.
Handles finite streams: HttpClient observables are finite, completing after emitting a single value (the response) or an error. This means that manual unsubscribing to prevent memory leaks is typically unnecessary, especially when using the async pipe in templates.