With software development, we are often presented with alternative choices for libraries and tools that appear to accomplish the same sort of thing...
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Doesn't it make more sense to
diffapplication state? And then only derive and update those parts of the view that need updating.Granted diffing the DOM is more abstract and could perhaps be more reusable across a larger range of applications but it's like preferring to catch the horse after it has left the barn rather than just locking the barn door. Maybe it's more to the point that VDOM-based solutions are more focused on providing an alternative to the DOM API that is as far removed from the DOM API as possible.
Good luck with that one.
Certain members of the front end developer community seem to have a hard time differentiating between a framework in general and an "application framework". There seems to be a "one word", "(my personal) one meaning" mentality out there.
I think the second one is even more problematic though - organization of what?
If you can get people to accept Web components as mere custom elements (while the existence of the shadow DOM suggests the DOM component perspective) I think people will quickly lose interest - especially as Safari only supports autonomous custom elements without a polyfill (or ponyfill).
I think not foreseeing the need for direct support of SSR/partial hydration may turn out to be the Achilles heel of the v1 spec. Hand designed solutions (that take over browser parsed DOM fragments) are possible with the technologies introduced by the spec but are not likely going to be embraced by a community with a very specific expectation of what a "component" should be.
… or components for that matter.
What I'm alluding to is that components boundaries need a lot more attention. You've published a number of articles about the performance impact of component boundaries but there is another aspect that I think needs more scrutiny.
On a legacy automotive engine a carburetor can be considered a "component". The way many front end framework components are authored is reminiscent of a small carburetor permanently joined to a slice of an engine block containing a single cylinder. When it comes to combustion engine design that idea would be considered ludicrous, yet in front end development this type of "self-containment" with high internal coupling is considered necessary to maximize productivity.
The Elm community gave up on "components" because of two distinct aspects of The Elm Architecture:
While both aspects communicate via the Model there is an important insight - the boundary around the part of state affected by a message often didn't match up with the boundary around the parts of state needed to render the affected parts of the view - thus making it impossible to package "a bit of View" together with a "bit of Update" (and therefore bit of Model) into a "self-contained component".
Now granted SolidJS's fine-grained reactivity gets around this by be being - well - fine-grained enough to not have to worry about these courser grained boundaries. But …
While framework components need to manage view state - shouldn't that be separate from client-side application state? This of course goes back to UI as an Afterthought which itself is based on earlier work. It seems to me that the current generation of "light weight" front end frameworks promote framework component boundaries that aren't necessarily ideal for maintainability - trading it off for perceived short-term productivity gain and perceived but usually unrealized reusability.
Great Article!
As I mentioned in my comment; doesn't it make even more sense to diff nothing, and instead react directly to the data changes?
Not all "data" is created equal.
UI as an Afterthought:
In the article state refers to state handled by MobX. So
I don't see the problem here. State changes -> you respond accordingly. If only a small part of your state changes, you could specifically respond to only those changes (and only update the UI where necessary, or not at all).
Because …
… because …
Current generation UI frameworks have a tendency to encourage client side architectures where "the UI is your application" - it typically takes a significant amount of discipline and effort to persevere with a "the UI is not your application" client side architecture.
Jest has pretty much shown the downsides of the "React is your application" architectural style. The testing framework is bloated and slow because that is what happens when you need to "unit test" "Smart UI Components".
Extreme Programming Explained (p.117, 2000):
This lead to the The Humble Dialog Box (more generally the Humble Object) back in 2002 - yet for some reason front end development 20 years later continues to ignore this insight:
Elm's update/view separation has a counterpart in the OO world - Command Query Separation. Traditional OO would argue the accessors and mutators belong on the same object because that object manages a single concern. Command Query Separation challenges that notion; it argues that updating state (via commands) and retrieving a representation of state (via queries) are separate concerns.
Similarly a dumb UI fragment is simply a representation (query result via subscription) of some part of the application state. That fragment may contain some simple actions (commands) to initiate a change of some part of application state - perhaps even a portion distinct from the part the original representation was based on.
jQuery projects typically ended up being a Big Ball of Mud because as a library jQuery made it extremely easy to work with the DOM, leading developers to try to solve all problems within the DOM. But the DOM was simply the representation of server application state as parsed by the browser - if you were doing anything interactive on the client side that representation might no be enough to rehydrate client side application state (that is what Embedding data in HTML is for). Client-side application state needed to be managed separately from the DOM and it's changes needed to be propagated to the DOM. Segregated DOM demonstrated that approach but by that point AngularJS and React already had all the attention.
Isn't that exactly what I'm proposing though? Having the data live in one place, and an mutation observer sitting on top of it changing the UI to reflect data changes. The data doesn't need to know about the UI and can live in its own little (testable) world.
User actions could then be passed back to the data as events, and suddenly the whole thing starts looking a lot like an MVC design. Or, if we want to look at it from the object side, we'd end up with two objects that communicate through message-passing, which is also an excellent way of de-coupling different parts of an application.
My interpretation of your statement is that you are proposing a variant of MVC where the mutation observer is intimately familiar with both the model and the view - i.e. is tightly coupled to both. The logic around such a mutation observer would be anything but so simple that it can't possibly break.
The point is to create the conditions where you don't need to microtest the dumb UI at all - delaying that part for integration testing.
Even Pattern-Oriented Software Architecture Vol.1 (1996) lists some hefty liabilities for MVC (p.142), in particular:
A consequence of the tight view/controller coupling is that with the controller being the most complex piece of the pattern a "dumb view/controller" becomes essentially impossible.
(p.136)
This is already is starting to look more like something like Flux where the "commands" become events or actions. The problem with the controller is that it orchestrates - orchestration logic tends to be complex. Sometimes choreography lets you break up that complexity into smaller more manageable pieces - ultimately that's what a state that accepts actions and supports change subscriptions is all about. That way an application can be built in terms of application actions and subscriptions to application events.
However in some cases the flux-style single global store just isn't optimal.
Aside: MVC: misunderstood for 37 years
So the ideal scenario is where "dumb UI fragments" can be updated via application event subscription (thin events requiring additional querying of the application to obtain relevant view state or fat events containing the relevant view state) and affect the application via application actions. The application gets to dictate the shape of the application events and application actions. The dumb UI depends on the application - not the other way around nor is there something (complex) sitting in the middle, brokering everything.
That MVC thing was a bit of an accidental red herring. Personally, I don't really like the idea of using MVC as a design philosophy on its own and only wanted to mention the similarity. More than the MVC part, I'd focus on the message-passing aspect of it, which to my knowledge is about the most decoupled way we know for two parts of a software system to interact.
Let's skip the controller part entirely for now, and just consider the data (model) and the UI (view): Ideally both would send very generic messages to the other, so neither would have to make any assumptions about the other.
But even in a more "real world" example, it will more often be the UI that will depend on certain assumptions about the data, not the other way around, which I find ideal.
This way, if we put the business logic on the data side (aka. coupling model and controller), we can reason about that side and test it independently of the UI.
The similarities to MVC are obviously still there, but more in the sense that it's a way to categorise components of our application, not a template for how to build it in the first place.
If any single paradigm could be used to describe this form of application structure, it'd be the original idea of Object Orientation (one that's more about message-passing and less about classes and inheritance).
That's not the mainstream perspective but the Joe Armstrong perspective:
And loitering here a bit subscribe-notify is a common communication pattern between BEAM processes as it decouples the Provider from the Subscriber. That is the relationship that you want between the application (Provider) and the dumb UI (Subscriber) in the context of UI updates. The beauty of that approach is that update logic doesn't have to know which parts of the UI are active to push updates out but only has to supply updates to the parts of the UI that are currently subscribed.
Aside: You may find David Khourshid's XActor interesting (and visit his Redux is half of a pattern articles while you're at it).
Not sure about the "generic message" and "no assumptions" aspects:
"The application" leads, the "dumb UI" has to follow.
That said there is also a Consumer Driven contract dynamic between the consumer "dumb UI" and the provider "application". The UI has to fulfil its intended purpose so the application has to make accommodations:
The aim isn't "loose coupling" but an application core that has no direct dependencies on the UI.
Nicolai M. Josuttis: p.9 SOA in Practice
i.e. we're investing in just enough complexity to keep the application decoupled from the UI - but no more.
There is that word again - component.
At least that's what the UML modeling glossary states.
😁
I am researching reactivity in general and a few reactive patterns (frp, push \ pull, and so on) for a few years already and I want to insist on a "reactive" definition.
Reactive programming is a pattern of delegating the responsibility of initialization data processing to the data source, which doesn't know dependent units and can't interact with it outside one-way notification.
FRP, OORP, Flux, two-way binding, single-store, granular updates are just buzzwords on top of that, other high order patterns.
Rx, Solid, React, Even Emmiter is all about reactive programming.
The main reason for that is to move components coupling from code to runtime, that's all.
I never thought about this before I listened to Rich Harris and his talk about rethinking reactivity where he explained how React uses the virtual DOM, and Svelte essentially uses hierarchical chaining (I'm not sure if there's a proper name for it but that sounds about right).
The reason it was so interesting to me is because if I didn't know what the virtual DOM was and someone asked me how I thought Reactivity worked, my instinct would be to describe a chain of dependencies for each object.
So basically having events for data changes?
Doesn't it suck that we have to make that tradeoff? I mean, both features are really really important for any app or site.
Why are SPA's naturally better at navigation experience? Because of animations, and relying more on replacing components on the page instead of forcing a full page change?
What is even a "page", in this case? When swapping out components, fluidly updating/morphing the UI bit by bit, when would/should a SPA decide to change the URL?
It's so complex. I'm starting to appreciate that there is a fundamental mismatch between the concepts of "documents/pages" and "application" which cannot simply be padded over by frameworks/libraries. The problem is exacerbated by the fact that to a consumer there isn't any material distinction between the two concepts (it's just a GUI), and sites often evolve into apps, as consulting clients want more and more features. Thus often invalidating any sound architectural trade-off one might have made in advance. In addition to the architectural complexities needed to be juggled by developers, who mostly really just want one single uniform way of working, which "just works".
Also, when reading about Resumability vs Replayability (re: Qwik), I wonder how approaches like Hotwire Turbo, which you mentioned, compare? Both Qwik and Hotwire seem to be DOM-centric.
Isn't Hotwire basically already "resumable"? Since Turbo Drive circumvents the need for rehydration, Turbo Streams reuses the server-rendered HTML, and Hotwire Stimulus also stores state within the HTML, and doesn't perform heavy bootstrapping or reconciliation? And how is Fine-Grained Lazy-Loading different from Turbo Frames?
Maybe @adamdbradley , @mhevery and/or @excid3 , @julianrubisch , @javan , @kirillplatonov could help clarify the similarities and differences between Qwik and Hotwire (specifically its Turbo and Stimulus parts).
The difference is that Qwik isn't saying everything needs to be rendered on the server. You can mix Turbo with Stimulus and get elements of this. But Turbo is more just a means of HTML partials. You could use that with any of the partial hydration approaches to have benefit of not shipping js to render it. But Marko or Qwik(and really modern js frameworks) are designed so the shift between hydration and client render is seamless.
I will say this html centric is a bit overplayed. I agree from a transport perspective but that can be in the form of inlined script tags etc.. unless you can solve double data which these aren't claiming you can achieve the same without resorting to what can be serialized as an attribute.
In general for what it is doing you can compare these with Turbo and all, but when it comes to app mental model and DX these are worlds apart. One feels like layering a Javascript app on server rendered views, the other feels like authoring a single app experience like you'd find with any JS Framework, ie React etc.
Thanks for clarifying it a little bit.
Hm. But Qwik, being an MPA, has server-side routing, like you said. It's client also focuses on "resuming" HTML rendered on the server, and is apparently also completely stateless. So why wouldn't everything be rendered on the server, then? What would be beneficial to render on the client? Animations (like on entry/exit)? Being stateless, does Qwik ever render anything on the client? To me it seems (from their github description, and blog posts) that SSR is not only Qwik's focus, but its fundamental mode of operation. I can't see how replacing sections of the DOM with SSR'ed HTML is any different (or more client-side rendering) than Turbo?
What do you mean by double data?
Yeah, the mental model seems quite different, and I appreciate that authoring components in React/SPA style is preferable DX to having HTML template partials which later has to be targeted from JS (Stimulus).
They have client state they just put it in the HTML, keep on reading and reflecting it back. Again I think they are just overplaying the it's just HTML thing a tiny bit. It's really no different than anything else other than by keeping it in the HTML they can pause and resume the same page multiple times (like if stored in service worker app cache). Of course limitations here around serialization and after render performance (constantly reading from the DOM/reflecting to the DOM is less than great overhead). One could obtain resumable hydration without doing anything HTML specific. All you need to do is serialize the props to every component to get the same. Of course that is wasteful, so a better approach is to look at it like a reactive data graph. Qwik does that and so could anyone else not doing exactly what Qwik does.
Qwik's approach could apply to a SPA with some refinement but they aren't focusing there right away. And I imagine given Builder.io static site generation will be the starting point. But look at their TodoMVC example Misko tends to show off. That is a very client side application. Each new Todo is client rendered, each removal and edit as well. Qwik only loads the event handlers you need and in so has incredibly granular hydration. But you write your TodoMVC app like a TodoMVC app for the most part. Think of Qwik's state more like a global store with Dependency Injection.
Qwik isn't doing HTML partials. It doesn't replace things from the server. I'm not sure where you got that idea from. It just hydrates out of order. So you could put a client side router on the page and not load it until someone clicks a link, yet before that happens do something interactive on the initial page. This is very applicable to SPAs. Now you could use Qwik with something like Turbo.
The "double data" problem is that technically the data gets serialized twice with hydration. Once in the HTML (ie your manifested view) and once as the data you bootstrap the framework with. I've seen experiments to extract the data back from the manifested view but that has big limitations, and it isn't what Qwik is doing. Their data in the HTML is just the data you may have serialized a different way and is still independent of the manifested DOM.
I was going to reply but, Ryan you are doing a great job, thank you.
Thanks for a good and candid response, as always, Ryan.
To complicate things a little bit further..
Compared to Turbo, you said:
I recently discovered Inertia.js. Which is like HOTwire Turbo (aka. Turbolinks) but sending JSON over the wire containing props data and the the name of the client side JS-component to inject it into. So that you could develop an SPA (using React/Vue/Svelte), with the same app mental model and DX, though also avoiding having an API. You get this by letting Inertia.js hot-swap components and data (props), and let the server take care of the routing. So it occupies this weird spot between an SPA and an MPA, since it, like Turbo, will "serve an MPA off a single page", as you said.
So Inertia uses client-side rendering (CSR/SPA) by default, and like Qwik is also saying "not everything needs to be rendered on the server". (Even though Inertia can even do SSR now.)
So how is Qwik different from Inertia.js?
To try to answer my own question:
I guess the main difference is that Qwik is able to Resume hydration of the initial HTML the server sends. While Inertia relies on React/Vue/Svelte to hydrate it by Replaying the application state on bootstrap / first page load.
So Qwik would have a faster initial Time-To-Interactive (TTI).
As you said:
So: partial page hydration.
But for subsequent interactions, then I guess it wouldn't be much of a difference. As Inertia doesn't do what NextJS SSR does. From what I understand, NextJS SSR serves a new page and then completely re-hydrates (replays) that page on the client, on every route change. (Unless using next-super-performance, which is a proof-of-concept that apparently does partial page hydration). Inertia, on the other hand, wouldn't need to re-hydrate (replay) components it swaps out, because it is responsible for rendering them in the first place.
It would be interesting to see an app that used Qwik with Inertia.js. It would, if my analysis is correct, speed up the initial page hydration, by allowing it to be SSR'ed and then simply Resumed on the client, allowing faster initial TTI. Inertia would then take over for subsequent page changes.
Feel free to correct me if I'm wrong anywhere.
On another note, @ryansolid:
It would also be really interesting if there existed a Inertia.js adapter for SolidJS.
The thing with Next and most SPAs is that they are fast after the fact because they render in the client. THe server only renders initially for the first load. The main awkward part of SPAs is that initial payload/hydration. You could make it work in MPA mode where it went back to the server but those frameworks don't optimize for that in general.
Now like we are seeing with React Server Components or Turbo there are cases where rendering partials on the server after the fact is beneficial, and in so those partials can also be partially hydrated. Which is interesting. But as soon as you have the ability to move this to the client the performance is better with client rendering. But there are other considerations here. I feel that thinking of this in a more microfrontend scope is where things like Turbo have more value. Or the fact that server rendering can save you from implementing an API.
But raw performance, client side rendering is probably going to win once you have the necessary JS in the browser. This is important. An impossible task on first load, but not so much after. You can of course do stupid things and cause waterfalls in the browser but just generally I see Turbo as a way to keep the MPA mentality going for client side routing. But other than the reasons I mentioned above SPA taking over is probably fine at that point. It's just harder to break things up in that manner.
So I'm still unclear where this goes. But there are a few things being overestimated right now. Lazy hydration just defers expense. You need to do it carefully. Like if a SPA did this and you clicked deep in the tree it would need to then load the whole page and hydrate, which would be terrible for the end user. Qwik avoids this by isolating the components hierarchically, whereas Marko today and Astro solve it by breaking off Islands. But naively implemented if you were to use Qwik in a SPA and you navigated since it suddenly finds itself needing to render everything in the browser it would be downloading a ton of small granular chunks that would have been better served as a single split bundle.
So if attacking this holistically I'd look at something in the middle where we can make the bundles large enough to not die by a 1000 slices but also defer work needed for hydration as needed. This is what we are doing with Marko and why we have a different focus. Because honestly while Turbo is probably good for the big stuff(page navigation) it sucks for the little stuff(small interactions). And might not even be needed for the big stuff if we do this properly except in those cases I was talking about.
We are also working on a streaming microfrontend setup with Marko that I guess could be Turbo-like but it's still something that you go to when you need it. But for now these are separate things and we are working on making Marko produce the smallest possible bundles and are in the process of implementing resumable hydration. Qwik is working towards it's similar goals. As is even Astro. I think we all acknowledge Turbo is a path but it's a bit longer term because there are so many gains to get already before going there and adding that complexity. Inertia.js is fine and all but I feel it is working from the assumption client frameworks have to be like Vue or React.. they don't.
I've always found the various approaches to reacting to data/state changes in JS frameworks rather over-engineered.
To me the ideal solution would be a
MutationObserverfor plain JS objects. Something that tells me (via callback) when, for example, an element was pushed on an array.Built-in reactivity on a data-level seems like a much more straight-forward (and probably easier to optimise) solution than a full re-render with subsequent DOM-diffing or Svelte's broken
update = () => state=state™ hackEDIT: To some extent, it is possible to approximate this behaviour in JavaScript using
Proxyobjects, which works just fine but comes with the downside of having to use Proxies of everything, because the plain object could still be changed without the proxy knowing.Even with this limitation though, I've found that this way of reacting to data changes is much easier to handle in plain JS and leads to way less weird shenanigans to convince a framework to really update.
Have you seen my library SolidJS? It's what I'm hinting at in the end about being more granular and diffing less. But it works as you mentioned more or less. I just don't want to always come in with the strong hand. But performance wise it is reasonably impressive.
Just wanted to say I think that SolidJS is fantastic work.
Very well written article, and kudos for staying in the middle on these discussions
At last a good article on dev.to, worth reading.
Not those kinds of "5 the best etc etc etc of 2021", or the "Top 10 ek ek ek of 2021"
JavaScript wins. Flawless victory. FATALITY