WTF is a HOT observable?

My modern Angular course: angularstart.com/
There seems to be some kind of important difference between "hot" and "cold" observables, but trying to grasp what that difference is can be confusing. This video aims to make hot observables easier to understand.
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0:00 Introduction
0:31 The Observer Pattern
1:59 Hot Observable (Subject)
4:18 Cold Observable
6:15 Recap
6:33 In RxJS
8:10 Gotchas
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[@JoshuaMorony]

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[@hansschenker]

Since we are on RUclips - you can Hot and Cold Observable explain with youtube videos watching:
- Cold Observable: 1 video title to 1 youtube user:
When you start a RUclips video - you are the only watcher (subscriber) of that video - when another user starts the same video title , he gets his own video playing from beginining
- Hot Observable: RUclips video streaming: 1 video stream - n possible users ( 0 to n subscriptions )
when you subscribe to a youtube video stream - you get the video stream from the time you subscribe to it (you could be late and get only the remaining streaming)

[@frontend3409]

hot: movie on cinema, cold: movie on netflix

[@hansschenker]

yes works also outside youtube
- cold: on demand for me (on netflix)
- hot: provided for whomever (provided anyway 0 or n cinema visitors (hopefully many )

[@fintechtelugu6980]

Wow ease explanation

[@3pleFly]

Joshua if you ever release a course on rxjs or even more advanced things in angular, I will buy it.

[@danielnaydenov9899]

You’re doing great content man. Keep up the good work ! I’ve been following you for a few months now and I love the way you explain things and the examples you back them up with. Your channel is like a “TS” - a superset of rxjs and reactive programming. Cheers ✌️🎄

[@dayronalfaro9461]

yes indeed, nice video morony this is a good place to learn or refresh our knowledge

[@3pleFly]

Always great to get more quality angular / rxjs content from you!!

[@DavidLacourt]

Wow exactly what I needed to understand my code! 🙏🏻 thanks

[@user-mg7fc5yu6y]

You are absolutely amazing!! Thanks a lot for the content :)

[@nakshi_ashik9181]

Man thank you, you just made something really confusing à lot less confusing, i'll definitely use this as à reference later.

[@darknight9185]

thanks you for creating such awesome video

[@SuperQuwertz]

Man, this is good stuff. Thank you so much!

[@samucancld]

Great content mate 👍

[@abhishekburagohain3796]

I always thought a cold observable is one that emits after at least one subscription whereas a hot emits regardless. Thanks for the explanation. Looking forward to more videos.

[@Ben-gq9tx]

@Abhishek Buragohain A hot Observable doesn't emit until subscribed either, it will just keep going *after* the last one unsubscribed 😉 Pretty easy to test with the angular httpClient (produces cold Observables) and pipe it to a shareReplay, making it hot.
The request fires only after the first subscribe

[@masumulu]

Tnx a lot, it was very helpful, Clean expression 👍

[@renugupta5985]

Your content is awesome. Thanks for sharing. Love from India.

[@alan614]

This was great!

[@rahulxdd]

Hi Joshhua, thank you for this video. Do you have a complete rxjs series?

[@JoshuaMorony]

I have a bunch of different RxJS videos on the channel but no proper "series"

[@devnullsrevenge]

Well said

[@TravisSomaroo]

Great video Josh! Where can I find this on your github repo?

[@colinstringer561]

Hey Josh, you seem to have missed the part where hot observables always emit values, and cold observables only emit once subscribed to?

[@JoshuaMorony]

I wouldn't think of it exactly that way and it depends on the exact context. If we are using something like share() on an HttpClient observable then the result will be a hot observable, but it won't actually trigger the observable logic until it is subscribed to.
If we are talking about a standard Subject as the hot observable, then nothing is triggered on subscribe because the logic to produce values is outside of the subject. This does allow us to trigger "next" even when there are no subscribers, but I don't know if it makes sense to think of it as always emitting because it won't actually be notifying any observers, we would essentially just be throwing values into the void. I would think of it more as that for a subject we are producing values independently of any subscribers to the subject.

[@CodingAbroad]

So an observable which is performing an http request would be a cold observable?

[@JoshuaMorony]

Yes, every time you subscribe to it the request will be re-executed (unless you are using shareReplay as well)

[@vitruvianeli]

The moment when you like the video in the middle, and then like it again at the end. But that second like basically unlikes it, so you press like button 3rd time :)

[@frontend3409]

that was... not easy.

[@Szergej33]

Use me as the Dislike button.
(Do not click it, this video was awesome)

[@CheesyOfCityOfHeroes]

rxjs = how to suck the fun out of coding.

[@JoshuaMorony]

no no no, it's just sucking out all of the fun race conditions, stale data, and imperative coding induced bugs!

[@_emnljrz]

@@JoshuaMorony agree, much easier to understand