how to use the observable function from the rxjs library in typescript

To use the Observable function from the rxjs library in TypeScript, we first need to install the library using npm. In the terminal, we can navigate to the project directory and run:

index.ts
npm install rxjs
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Once installed, we can import the necessary classes and functions from the rxjs library. Here's an example:

index.ts
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

const numbersObservable = new Observable<number>(subscriber => {
  subscriber.next(1);
  subscriber.next(2);
  subscriber.next(3);
  subscriber.complete();
});

numbersObservable.pipe(
  map(num => num * 2)
).subscribe(
  result => console.log(result),
  error => console.error(error),
  () => console.log('Complete')
);

// Output: 
// 2 
// 4 
// 6 
// Complete
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In the code above, we create an observable that emits the numbers 1, 2 and 3, then completes. We use the pipe function to apply a map operator that multiplies each emitted number by 2. Finally, we subscribe to the observable and log the output using the console.log and console.error functions.

By using the RxJS library, we can create powerful asynchronous programs with clear, functional code.