defer

type defer = <T>(fn: () => T) => Observable<T extends Promise<infer R> ? R : T>

f():      ---a
defer(f): ---a|

Creates an Observable that executes provided fn on subscribe and uses it's result. Handles async functions, emitting upon resolution. This is similar to the fromPromise method, but allows to delay an execution of heavy operation until the subscription happens.

import { defer } from 'light-observable/observable'

const fetchNumbers = defer(() => Promise.resolve(1))
fetchNumbers.subscribe(console.log)
/*
 -> 1
*/