Observables and Promises are both constructs used for handling asynchronous operations in JavaScript, but they have some key differences. Here are the main differences between Observables and Promises: 1. Multiple Values vs. Single Value: An Observable is a stream of values that can emit multiple values over time. It can represent ongoing processes, such as user events or data streams from servers. In contrast, a Promise represents a single value that will be available in the future once the asynchronous operation is completed. 2. Eager vs. Lazy Evaluation: Promises are eager, meaning they start executing immediately upon creation. When a Promise is created, it initiates the asynchronous operation right away. On the other hand, Observables are lazy, meaning they do not start producing values until someone subscribes to them. 3. Cancellation: Observables can be canceled by unsubscribing from them. This allows you to stop receiving values from an Observable and clean up resources. Promises, once initiated, cannot be canceled. 4. Composition: Observables have powerful composition operators that allow you to transform, combine, and manipulate streams of values easily. Operators like `map`, `filter`, `merge`, and `combineLatest` provide a declarative way to work with asynchronous data. Promises, on the other hand, have limited composition capabilities and typically rely on chaining `then` and `catch` methods. 5. Error Handling: Promises handle errors using the `catch` method, allowing you to handle errors in a centralized manner. Observables, however, provide more advanced error handling mechanisms, such as the `catchError` operator, which allows you to handle errors at various points in the stream. 6. Time: Observables can handle time-related operations more easily, including scheduling and delaying emissions of values. Promises do not have built-in features for handling time-related operations. Overall, Promises are simpler and more straightforward for handling single asynchronous operations with a single result. Observables are more powerful and flexible, suitable for handling streams of values, ongoing processes, and complex asynchronous scenarios. They provide more fine-grained control, composition capabilities, and advanced features for handling asynchronous data. Here's a comparison between Observables and Promises with examples: Example using Promises: 

function fetchData() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('Data fetched successfully');
      // OR
      // reject(new Error('Failed to fetch data'));
    }, 2000);
  });
}

fetchData()
  .then(data => {
    console.log(data);
  })
  .catch(error => {
    console.error(error);
  });
In this example, the `fetchData` function returns a Promise that resolves with the message `'Data fetched successfully'` after a delay of 2 seconds. The `then` method is used to handle the successful result, and the `catch` method is used to handle any errors that occur. Example using Observables: 

import { Observable } from 'rxjs';

function fetchData() {
  return new Observable(observer => {
    setTimeout(() => {
      observer.next('Data fetched successfully');
      // OR
      // observer.error(new Error('Failed to fetch data'));
      // OR
      // observer.complete();
    }, 2000);
  });
}

const subscription = fetchData().subscribe(
  data => {
    console.log(data);
  },
  error => {
    console.error(error);
  },
  () => {
    console.log('Observable completed');
  }
);

// Unsubscribe after 3 seconds
setTimeout(() => {
  subscription.unsubscribe();
}, 3000);
In this example, the `fetchData` function returns an Observable that emits the message `'Data fetched successfully'` after a delay of 2 seconds. The `subscribe` method is used to handle the emitted values, errors, and completion. The `unsubscribe` method is used to cancel the subscription after 3 seconds.