from 

Function from will turn an iterable, Promise, or Observable-like value into an Observable. Examples using iterable:

A stream from an array

const { rxObserver } = require('api/v0.3');
const { from } = require('rxjs');

from([ 5, 10, 20 ])
  .subscribe(rxObserver('from([5, 10, 20])'));

And from a string

const { rxObserver } = require('api/v0.3');
const { from } = require('rxjs');

from('Hello')
  .subscribe(rxObserver(`from('Hello')`));

For promise conversion example see fromPromise