JavaScript Symbols - HTTP203
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- เผยแพร่เมื่อ 19 มี.ค. 2018
- Jake Archibald explains JavaScript Symbols to Surma in 2 minutes. What do you use them for!? Why!? All will be revealed... #HTTP203
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It will be great if you guys will show a "real world" implementation examples of what you're explaining!
As a newer developer, I feel that these type of videos would be way more useful with live code examples, rather than just strict conversation. I realize that the point may be to have your audience go and research on their own, but in the moment being able to see an example would be more helpful in my opinion.
You're not the first to say this, and it's something we're going to try at the next recording.
I dunno I really enjoy this format. It's kind of like an appetizer that either fails to interest me, or makes me curious enough to go research the topic on my own.
I think the 2 minute format might not necessarily lend itself too well to spend too much time doing code demos and the like. Still, if they do adopt code examples I'd be curious as to how they'd pull that off.
I'm interested to see how we pull it off too! We'll still do the podcast, which doesn't rely on visuals.
Well, as a non-english speaking creature, I find it more difficult to grasp all the subtleties of the topics you might talk about. This is even worse with the podcast ; that's why a video with examples would be better and would provide concrete use cases.
This video is a good example, because I never know when to use Symbols (I tried in a class to hide properties but it was useless since we can ask an object to list its Symbols). The only use case I can see if I want to manually define an Iterator.
Thanks for the good work though, it's always a pleasure to see you both chatting.
JavaScript Symbols! What do you use them for? Do you use them for anything? Let's find out!
Enrique M. Mr peanutbutter?
Guys, you are doing great and thanks for uploading these videos. if possible, could you pls add few code examples with the dicussion.
We are gonna attempt to solve this the next time we record :)
I'm a super fan of #HTTP203. You are my favorite youtubers. 👍
Anyone have more information regarding Symbols across s?
Here's a link to the blog post I think they talked about: jakearchibald.com/2017/arrays-symbols-realms/
I found it in the episode notes for the full podcast here:
developers.google.com/web/shows/http203/podcast/
TY!
i didnt know about this -symbol-for-sharing-thing... interesting!
I've always felt that Symbols were most useful with "native" (well-known) ones, like Symbol.iterator as you mentioned.
For the rest, I still have to find a solid use case.
Non-enumerable properties? Object.defineProperty got us covered.
Private properties? Not really, since we have Object.getOwnPropertySymbols and Reflect.ownKeys.
Moreover, symbols aren't really polyfillable, so you can't use them if you have to support IE.
Does anyone have any experience with symbols outside the well-known ones?
I'd like to watch something about proxies soon!
Noted!
203? That's Numberwang!
Steffen Bruchmann www.google.co.uk/search?q=numberwang
More on symbols please!
2.years gone since this. Video has been uploaded and no more symbols has been seen
So it's all going to change soon. What a surprise.
I don't think it's going to change.
Like your glasses!
What about dart?
No.
I would like a medium Fries and a double Cheese Burger. Thank you
Royale with cheese?
Symbols are hidden not because they are not enumerable, but since from es2015 keys now are divided into 2 categories:
1. names
2. symbols
So all the methods that already existed by then only take into account names. There is a big problem with nomenclature, since some old method names use "key" or "keys" but it's no longer correct.
So, let's take a look from the spec to Object.keys (www.ecma-international.org/ecma-262/7.0/#sec-object.keys):
> When the keys function is called with argument O, the following steps are taken:
>
> 1. Let obj be ? ToObject(O).
> 2. Let nameList be ? EnumerableOwnNames(obj).
> 3. Return CreateArrayFromList(nameList).
>
> If an implementation defines a specific order of enumeration for the for-in statement, the same order must be used for the elements of the array returned in step 3.
So, what it's taken into account is the result of EnumerableOwnNames (www.ecma-international.org/ecma-262/7.0/#sec-enumerableownnames), let's have a look to it:
> When the abstract operation EnumerableOwnNames is called with Object O, the following steps are taken:
>
> 1. Assert: Type(O) is Object.
> 2. Let ownKeys be ? O.[[OwnPropertyKeys]]().
> 3. Let names be a new empty List.
> 4. Repeat, for each element key of ownKeys in List order
> a. If Type(key) is String, then
> i. Let desc be ? O.[[GetOwnProperty]](key).
> ii. If desc is not undefined, then
> 1. If desc.[[Enumerable]] is true, append key to names.
> 5. Order the elements of names so they are in the same relative order as would be produced by the Iterator that would be returned if the EnumerateObjectProperties internal method was invoked with O.
> 6. Return names.
So as we can see here, there one main concept: keys, which they can be symbols, or names (strings), and Object.keys, and a lot of methods from es5 and below use EnumerableOwnNames algorithm to get the names (not well named "keys").
TL;DR
No matter that both are keys, symbols shouldn't be confused with names, since these last ones are strings, so we have to check from the spec the method that we would like to use to see what considers to be a key, if it's talking about names (strings) or symbols.
Yep. That's why they're useful for iterator callbacks, rather than using a name like toJSON. But they aren't hidden due to developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertySymbols
Jake Archibald I just wanted to comment that they aren't hidden because they are not enumerable, but because they aren't taken into account by old methods and new ones that were skipped on purpose. The thing is that on the video you agree that the hiddeness reason is enumerability, and I believe this could confuse some people...
I say "it's kinda hidden *and* it's not enumerable", but I suppose it's possible to mistake the "and" for "because".
I know that it's impossible to explain in depth any concept in that short time, and your videos are amazing, but in this particular case I believe enumerability shouldn't have ever mentioned, since it doesn't have to do with symbols hiddeness, and IMHO in the video this is the reason you agree is promoting that
My intent wasn't to promote hiddenness. The benefit is things like Symbol.iterator & co, vs why obj.toJSON isn't great.
So a symbol is a singleton.
no
It always felt like a worse supported weakmap to me.
I can’t quite follow. WeakMaps are something completely independent of symbols.
In the end, they allow you to do pretty much the same thing, don't they?Adding extra information to an object that you can only access when you have access to the weakmap / symbol that was used.
Aside from the built in well-known symbols, which you can't replace with WeakMap, I don't really see a difference between them except obviously their Syntax.
Pesthuf You can always get the reference to a symbol with Objet.getOwnPropertySymbols, so no, WeakMaps are a totally different thing.
I guess most of the value of symbols is exposing some of the internals of JavaScript to developers, so they can "hack" their way with operators and methods like instanceof, for...of, concat() and so on.
Thanks, I didn't know about Object.getOwnPropertySymbols at all. I had always assumed (and I think even read) that because Symbols are unique, they are also secret (unless it's exposed with Symbol.for or a module).
That's pretty neat,. then. Guess they are actually pretty useful and unique.
HTTP203 videos are now boring 😪
What makes you say that? I am interested in your feedback.
the interruptions are too many so i dont really get the main point clearly
...and everyone wants to dance to the alarm..lol
I hear you with the interruptions. I have noticed that myself and it’s something I wanna work on in the next recording :D I hope that will solve your second point as well. The dancing will continue tho. In fact, it’ll get worse. Probably.