Is the only difference between Observable.of and Observable.from the arguments format? Like the Function.prototype.call and Function.prototype.apply?
Observable.of(1,2,3).subscribe(() => {})
Observable.from([1,2,3]).subscribe(() => {})
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85
Not quite. When passing an array to Observable.from, the only difference between it and Observable.of is the way the arguments are passed.
However, Observable.from will accept an argument that is
a subscribable object, a Promise, an Observable-like, an Array, an iterable or an array-like object to be converted
There is no similar behaviour for Observable.of - which always accepts only values and performs no conversion.
145
It is important to note the difference between of and from when passing an array-like structure (including strings):
Observable.of([1, 2, 3]).subscribe(x => console.log(x));
would print the whole array at once.
On the other hand,
Observable.from([1, 2, 3]).subscribe(x => console.log(x));
prints the elements 1 by 1.
For strings the behaviour is the same, but at character level.
- What if Observable.of(1, 2, 3).subscribe(x => console.log(x)); – xiaoke Sep 14 '17 at 22:28
- @xiaoke Then surely it is 3 separate emissions (1, then 2, then 3). – Tsvetan Ovedenski Sep 15 '17 at 6:40
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Another interesting fact is Observable.of([]) will be an empty array when you subscribe to it. Where as when you subscribe to Observable.from([]) you wont get any value.
This is important when you do a consecutive saving with switchmap. Ex:
.do((data) => {
this.jobService.save$.next(this.job.id);
})
.switchMap(() => this.jobService.addSites(this.job.id, this.sites)
.flatMap((data) => {
if (data.length > 0) {
// get observables for saving
return Observable.forkJoin(jobSiteObservables);
} else {
**return Observable.of([]);**
}
})).do((result) => {
// ..
})
.switchMap(() => this.saveComments())
....
if data.length = 0 in addSite section, the above code is returning Observable.of([]) and then goes to save comments. But if you replace it with Observable.from([]), the succeeding methods will not get called.
