What are observable creation functions?

RxJS provides creation functions for the process of creating observables from things such as promises, events, timers and Ajax requests. Let us explain each of them with an example, 1. Create an observable from a promise

    import { from } from 'rxjs'; // from function
    const data = from(fetch('/api/endpoint')); //Created from Promise
    data.subscribe({
     next(response) { console.log(response); },
     error(err) { console.error('Error: ' + err); },
     complete() { console.log('Completed'); }
    });

2. Create an observable that creates an AJAX request

    import { ajax } from 'rxjs/ajax'; // ajax function
    const apiData = ajax('/api/data'); // Created from AJAX request
    // Subscribe to create the request
    apiData.subscribe(res => console.log(res.status, res.response));

3. Create an observable from a counter

    import { interval } from 'rxjs'; // interval function
    const secondsCounter = interval(1000); // Created from Counter value
    secondsCounter.subscribe(n =>
      console.log(`Counter value: ${n}`));

4. Create an observable from an event

    import { fromEvent } from 'rxjs';
    const el = document.getElementById('custom-element');
    const mouseMoves = fromEvent(el, 'mousemove');
    const subscription = mouseMoves.subscribe((e: MouseEvent) => {
      console.log(`Coordnitaes of mouse pointer: ${e.clientX} * ${e.clientY}`);
      });