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086: Routing in Ember with Alex Matchneer

Hosted byCharles Lowell

October 19th, 2017.

Alex Matchneer: @machty | FutureProof Retail

Show Notes:

Charles and Alex Matchneer have a great discussion that centers around routing in Ember.js: what they want to see in a router, what problems it solves, what’s wrong with the routing solutions we currently have, and what the ideal future looks like in respect to routing.



CHARLES: Hello everybody and welcome to The Frontside Podcast, Episode #86. My name is Charles Lowell, your developer here at the Frontside and podcast host-in-training. I'm flying solo today. It's been a while but that's okay because I've got a really fantastic guest on. Actually, we debated this at the beginning of the show, whether this was the third or the fourth time he's actually been on but no times are too many so hello, Alex Matchneer. Welcome back to the podcast.

ALEX: Thank you. It's great to be back.

CHARLES: You're still at the same place that you were the last time.

ALEX: Yeah. Still working at FutureProof Retail. I'm still working on bunch of mobile ember-cordova apps and that's definitely occupying on my time.

CHARLES: Nice. Because FutureProof Retail has a large hardware component and we were doing a series on IoT, we were originally going to have you on the show to actually talk about that experience of what it's like to be a part of a startup and develop software that's going to be running on a bunch of devices and the unique set of problems that poses. But in the pre-show, we decided to scrap that because there's actually a topic that we're both very interested in and you've been heavily involved in lately and might be a really interesting preview as to what's coming in the Ember community and at large.

Today we're actually going to go back to talking about the same subject that we talked about in our first podcast, which is routing: what we want to see in a router, what problems does it solve, what's wrong with the routing solutions that we have today. Talk about what that beautiful, ideal future that we want to live in looks like with respect to routing. You've been thinking about this a lot lately. What have you been thinking?

ALEX: I'm an Ember core team emeritus and back when I was on it and I'm a lot more active, I did a lot of work on the router, particularly with how it handles asynchronously loading data when you click on links and go to different sections of your app. I spend a lot of time over the last three or four years figuring out the nice patterns for what you actually want to use if you're building out lots of Ember apps. Then kind of around that time, right after landing some cool stuff and some not cool such us query params, which has been a challenging aspect, I start working at this company FutureProof Retail that is like 90% of the Ember work that I do there is in mobile apps.

We use Cordova so we're basically running these apps inside a web view, inside either iOS or Android so that we can stay with the technologies we are most familiar with, such as JavaScript and CSS and HTML and build apps using that. We can use Ember to do that. What I found was that I couldn't really apply a lot of the same patterns, all these nice conventions that Ember router gives you. I couldn't really find a way to map that onto what I need to build in mobile apps and there's a few different reasons.

I got really busy with the startup, just trying to build these things and kind of went off the happy path where I really just couldn't find a way to make it look like an Ember app. One of the nice things about the whole points of convention over configuration as this sort of Ember and Rails philosophy is that, one of the benefits is that if you know Ember and know Rails, you can drop into someone else's apps as long they're following these basic conventions and immediately know how to be productive and know how it's structured, know how to make a change to it and have it maintain a convention and not just have everybody who's using some framework build these totally different apps from each other that have no shared conventions and whatnot.

Everyone is supposed to be able to learn from each other, grow with each other as long as they stay with these conventions. I couldn't really find out how to stay within Ember conventions and build this mobile apps. For a long time, I just didn't really contribute too much to the Ember router at all. I kind of fell out of touch with how most people are using it because most people are building these desktop-centric apps and here I am working on these mobile apps after three years.

CHARLES: What are some of the specific use cases that were just impossible to, or not impossible but presented a challenge?

ALEX: The first one is which is I think is actually one of the easier problems to solve but still some challenging is that you want something that's called stack routing or stack navigation in a mobile app, which is if you're actually building a native iOS app or an Android app, they both have different names for how they provide you this. But you're thinking of things in terms of stacks. In Android, you might open another activity, which is a full frame of a page in your app and you can push it and then when you press the back button, which is built in in Android phones, it'll pop that off the stack and take you back to where you were.

In iOS, they give you a UI navigation controller and let you push and pop view controllers and that is how they want you to think about these applications. That is contrasting to what Ember makes you think about, which is go and define your static hierarchy of all the different places that you can be in an app. But with stack-based navigation, you don't necessarily know upfront all the different orderings of which frames are going to be pushed onto what and you might have situations where you want to be able to dynamically push, say an 'Add a Credit Card' page to where you are and maybe it depends on some data that's been loaded at some lower level in the stack and you can't model that as nested routes in the way that you might think about it in classic Ember apps. It's a different structure --

CHARLES: Now, when you say lower in the stack, I'm curious, if you're entered in aren't you... Oh, you mean... I see, previously in the stack. Okay, so lower in the stack so you're thinking like your current position is at the top of the stack.

ALEX: Right, yeah.

CHARLES: I see. Now, let me just clarify this in my own head. Your Ember routing structure is ultimately realizes a static tree but at any moment, you are entered into one path through that tree so you do have something resembling a stack. It's just is it the pathways that the ways that you can actually get nodes onto the top of the stack is you're limited because that can't be dynamic.

ALEX: Yeah, but even then, it's hard to describe what the difference is but the kind of stack that you're thinking of in terms of the classic Ember router map is more like you're in these different substates than you are different frames that you've pushed onto your --

CHARLES: There's a finite and fully enumerated set of next states.

ALEX: Right. To be very concrete, if you have a post route and then a post show route and then a comments route under that and these are all nested in a row, then if you're in the comments route, you are in a kind of hierarchical stack that might have loaded the post that you're looking at and maybe the post call-to-action above that and the comments for that but you're still in one thing. You've just expressed that one thing in terms of these substates so that every other state that's in the parent state can share the same data loading. That's different from saying, "I'm on this page and now, I want to push another page on it and maybe tap some of the data that has been loaded on previous pages." That's more of a navigation stack in a hierarchical substates stack.

CHARLES: Is the difference then, the data dependency? Because if you think of the Ember classic where you got the static tree, at least theoretically all of the data in the leaf nodes depends on the data that's above. It's not just being able to dynamically push stuff onto the new stack but it's also saying, you want to be able to push stuff that might have no dependency on the stuff further up and it doesn't need to be re-rendered if stuff further up the stack changes.

ALEX: Correct.

CHARLES: But sometimes it might.

ALEX: Right so there are a lot of corner cases that come out if you try to model this new way that a lot of corner cases have been thought out of if everything matched nicely to this hierarchical substate classic Ember stack but not for navigation. If you want to do something that's stacked routing-based, I've had a few different approaches. At our company, we maintain a suite of different apps that are sort of retailer or grocery-centric and the first one we did, which is more popular flagship one is Mobile Checkout, which is an app that lets you going to stores, scan items with your phone and checkout and skip the cashier line, which is great if there's huge lines and you just want to buy a little handful of things or maybe in your shopping cart. But that is like any other mobile app is really conducive to this step navigation approach.

Then we had to make a few apps after that such as like another app that is [inaudible] do a manual check then ordering app and other of handful things that you can imagine is might be used on a grocery store. I took the opportunity to like, "I don't really like how the routing turn out the main mobile checkout shopper apps so let's try different things." If you approaches, at least have their pros and cons without really feeling you're solving the problem and one is to maintain your own in-memory stack of where you were, every link to you, you might recall where you were and then use that logic in addition to what's in a URL to decide what transitions to make, which to use Liquid Fire for that.

But already, there's these weird growing questions like, "Why are you even using the URL? Is it helping you at all?" That was the main issue with the main app that we did. The other approach was to try and not even use any of the 'router.map' stuff at all. I use the router.map to basically just create one wildcard route. You can use normal Ember to use it like '*half' and that basically collects the rest of the URL as a param that you can use to do whatever you want with. I was using that to basically pass to another, which is internally used by Ember to do the stack-based parsing like grab a little bit of the URL and then parse the param for that then grab another.

Every time you could see your stack in the URL. That has its benefits but the worst part about it is that it's getting further away from Ember so any add on that you might want to use at Internet of Things in terms of which route you're in and has conventions like that you just can't use. I can't think of a good example at the top my head but it's like the further you get away from those norms, the less the Ember system can help you and on your own building your own framework.

This is all to say that I think I have enough experience at this point to bring home some of the things to Ember and I'm excited to get back into contributing to Ember with this one particular thing that I'm focusing on now, which is... I don't even know what to call it. It's like --

CHARLES: What does it do? The route stuff?

ALEX: It's route stuff. Actually, let me get into the other... That's what is tricky about stack routing and tricky to sort of, if you already have to go through a mental hurdle with thinking of the Ember router and as a stack of states or substates and you train your brain to think that way, it's really hard to take yourself out of it and realize that what you're trying to build with like a classic mobile navigation is almost looks like the same thing but it's really different.

The other challenging problem, which is specific to our particular app is that you wouldn't think of it as a very heavily server-driven app but if you're writing an application that at any point can get a message from the server like, "Hey, your status has changed," and that state is heavily coupled to navigation of where you're allowed to be in your apps for the state of some certain model, then you're going to have a really hard time, I'd say in modeling an Ember. I have a really hard time convincing people of this until they've actually tried to do it themselves, which is why I'm going off and just building things showing people.

CHARLES: You don't have to convince me because I think one of the biggest problems is the router is like the one non-reactive piece of Ember, which is unfortunate because it's essentially, what is the equivalent of the Redux store in a Redux application, where it's the state that drives literally the entire application and yet, any type of non-hash change driven updates, you have to manually manage. Every time that we've done it, it's been a problem and depends on what data, at that point you have to be very thoughtful because, at least from the highest level, if there's damage to a piece of the tree higher up, you need to realize those effects of that damage or that change all the way down the tree.

ALEX: Exactly. That is a great way of putting it. This is maybe a good time to mention this thing called ember-rideshare. I've had a really hard time describing these problems to people so I figured what I would do is write this blog a few months back, a little article called ember-rideshare. It's just a given name to the kind of app that still really hard to write in Ember. It's a mobile app. It involves stack routing but the other part is really difficult about it is this problem of the router being in a silo.

It is reactive but it's only reactive to that URL. Other things changes, they need to, like you said come in and patch up something else about the router in case you add some URL that is no longer able to present some model of whose status changed. That's an article on a blog that I can probably link to in show notes or something. When I talk about ember-rideshare, imagine using Ember to build Uber or Lyft and it's got just the slightest bit of the whole thing. The whole point of the app is to coordinate your client-side request of I want to ride with the server going off and doing a bunch of things and finding a nearby driver, displaying you bunch of driver locations and it'll show up. Then finally, find you a driver. It's a constant communication.

Throughout that point, you can sort of imagine modeling all the different screens as routes but the routes that are actually allowed to see at any given time are heavily dependent on what is the current state of the user's current ride. But you shouldn't be able to go to a route that says like 'cancel ride request,' if you haven't requested a ride in a million of these other things. If you're an Ember developer and you think that's an easy problem to solve, you're probably thinking, "I would use before model hook when I'm entering that route to check the state of the model," and if it doesn't make sense for the route of entering, I want to transition elsewhere.

That's fine. That's good if you're doing an app if the user is the one deciding where to navigate to. But then when you're on a route like that and then the server tells you that your ride is done, you can't still be on that route so you've got to have some kind of validations that is like, "This is no longer a valid route to be in. Is the user still in this route?"

CHARLES: "Where am I going?"

ALEX: Yeah. Before model doesn't really help you. It's this one-shot discrete event and you just can't capture all the different things. The ember-rideshare describes some of these problems a little bit more detail but that's the main issue with it. Like you said, what is actually missing about the router? Maybe it's reactive but it's only reactive to the URL, what about all these other things that are happening into your app? I think there's a handful of APIs in Ember that they're great but they're kind of siloed off in a way. If you want to make two different kinds of worlds meet, you've got to write a bunch of your own code yourself or you just have to do mentally going back and forth and being like, "I did this, so I can't use this kind of API."

I did a lot of work on the Named Blocks RFC, which previously there is silos between if you're passing blocks to a component versus data, you've got to think about them differently and all the ways that you might forward that data to a different internal component, if you want to build these composable, reasonable internals, you got to be kind of split-brain about it. I feel the same way about how the Ember router works. It's only good at dealing with stuff that has to do with the URL and you're on your own, if you needed to react to data changing. That's what I'm trying to fix. Does that correlate with your experience of working on Ember stuff as well?

CHARLES: Absolutely. I think that's a great way to put it. I think we've come to a consensus of the problem statement. I am curious to see a big separate query params. I'm going to throw that wildcard out there or maybe we should save it for later.

ALEX: Yeah, I definitely going to come back to it. If I say all this cool stuff and I still don't have a solution to that, then what am I talking about?


ALEX: Which to be honest, I haven't thought of every single possible thing. I'm doing the thing where I talk about it on a podcast that everyone can guilt me into really finishing it. I actually really think that I'm going to finish it. I'm very confident in stuff I'm working on. I'm very excited to bring it to people but it is not all 100% fleshed out and I definitely appreciate anyone's help to those interested, understands the nature of the problem and wants to help me work on some of this stuff and like that, in Ember community Slack or wherever.

CHARLES: Yeah, I'm really excited to hear it and see in what ways we might be able to contribute.

ALEX: Basically, the goal is to find some underlying primitives that can model the current behavior without mistake because obviously, we can introduce something that's going to break into Ember apps. Basically, to recognize that the URL is something that goes through multiple passes of transformation, to eventually become the thing that displays stuff on your screen, from the very foundation of it, and this is the actual mini-course of what Ember router does internally because it involves a few different libraries and maybe this is a re-hash from the podcast that I did with you guys but --

CHARLES: Can I just say that there are some things that the Ember router really does right, that are fantastic? One of those things is it baked in to every single piece of data. It doesn't do the stack but in that tree that it models, every single node in that tree abstracts away the asynchrony of that node. I think that's absolutely huge so you get both the dependency enumerated like these are the things that I need to marshal the data to render myself and it's implicit that it might take some time. I might need to draw on a couple of different things to actually assemble this data so the asynchronous nature is modeled up front and it's implicit and it's there every single time, which turns out to be the right thing.

The sampling that I've missed has been an excruciating void in all the other routing solutions that I've tried outside of the Ember community is that they just punt over asynchrony to you. You deal with it, not our problem and it's like, "Actually, that is the problem." Anyway...

ALEX: That's a great point because if the router doesn't help you with any of this stuff at all, then it basically means that every one of your pages that you might want to render after the fact, probably has to have some loading logic like if data is loading, show us spinner. Otherwise, here's all the data --

CHARLES: Yeah, if something happen wrong.

ALEX: Right and sometimes that is actually what you want to do. Sometimes you want to do these skeletal in UIs that looked like the page that's about to display but the date isn't there yet so everything is, regardless going to be wrapped in these 'if' statements, 'else' statements. I worked in ember-concurrency and some people are using that to basically move more of that loading into controllers, that's fine. If that's what you're actually trying to do and that's what you're opting into, that's a perfectly reasonable solution but most of times, chances are you're entering a route and you don't want to have to teach the entire template tree underneath it that has to handle all these different states.

There's these nice ideas that work in some cases and I'd like to make them work in more cases than Ember helps with and a whole loading all the promises and the model hooks and absolutely going into the loading state are really cool primitives that Ember is going to do for you. The other frameworks, they don't try to be opinionated. They won't do any of that for you. Sounds like you ran into that with some of your React stuff?

CHARLES: Yeah. I definitely did. There's just not much help when you actually want to model asynchrony. You can do it. It's pretty easy. You just implement the right hooks or model a series of actions, either with a Saga or Epic, if you're using redux-observable. But again, you have to assemble it by hand and you have to generate those abstractions by hand and you just want to have them at hand already and not have to worry about that.

But the advantage, though is that generally those ones that you do have at hand or that you generate are fully reactive. If new information comes that's germane to that particular leaf in the tree or that particular note in the tree, there's no difference between the initial state and the update state. Whereas, in Ember, you got your first shot and then that data is now at rest.

ALEX: Right. I definitely have been looking at React router, in particularly v4. I think it's all contentious for people to see it at first but being able to put things like in your render function, you can say, "If this data is present, something that's going to be past and be a prop or something," then show a loading spinner or otherwise, start matching these subroutes. That's really cool. That's expense that you can't look at essential map of all the states of your router can be in but that's also a real problem and if you can demonstrates that the state world is not in a separate silo than the routing world.

CHARLES: With great power comes a lot of bugs. You do run into a lot of things where you have rogue matching. You have random things that are inside your view tree that are matching against the route and they just render and you have to be very careful because it's almost the difference between blacklisting and whitelisting. I see what you're saying. It could be confusing.

ALEX: Yeah. I think it's definitely a tradeoff. I think if I had something like a match, I might have been able to maybe arrive at a stack routing solution a little earlier. I'm not sure about that. It's definitely something that could be handled by React router. I think one of things that React and React routers better at in general is that everything is, more or less a component that is more easily swappable or something else here. You're not going to have as many of those silos and I really do think, it went through a lot of churn and maybe, some people had trouble, maybe a lot of people, I don't know had trouble kind of following all the major versions. But I think React router Version 4 is pretty damn cool. I think there's a fullest realization of that kind of modular mindset.

CHARLES: I think the biggest problem I have with it, though is it requires the view tree to model your routing structure. That bothers me. I feel like you could do the exact same thing. You could have a way to express your routes, not necessarily with a separate routing file. I supposed you could do it with JSX or something but actually have it be kind of orthogonal to your view tree. The way you can model this dynamically updating thing that can match against anything and maybe, even express it all in one place. Although once you get a big tree, it could be hard to control that.

The part that I've come into most conflict and maybe who knows, maybe I just haven't used it enough, we've only got one application that we're using the router V4 on. But the fact that it's actually in the view tree, it bothers me. It's in the state objects. It's hard to adapt to Redux because that state is opaque. It's the routers controlling it and I would it to be not have to pass through React components but just be like, give me the firehose of the router state.

ALEX: Right. I love what you're saying. If I'm going to bring this stuff to Ember, I can't suddenly make it work like matching within the view tree. That's not what I'm working at or proposing here. All the stuff is basically to empower that firehose to respond to more things that can drives views and respond to them in a live way, not like a one-shot async validation, only when you enter.

CHARLES: Maybe this is what the problem that you're trying to solve and one of the things it's really nice to be able to match against anything inside the view tree is that Ember's rendering process of a route is very opaque. The process, by which an outlet gets connected, that's not something that you really have much visibility into. Is that a good statement of the problem?

ALEX: That's definitely part of it. You definitely have to go to the documents. I think it's telling that --

CHARLES: I've never done it. I don't really know how that works and I've written a lot of Ember code.

ALEX: How what works?

CHARLES: How the route gets rendered, like the mechanics around, which I understand how the route object actually, you makes the decision to render its template and do all that stuff. I know it as a user but I don't know the mechanics and I wouldn't know how to extend it.

ALEX: I'm not sure if the stuff I'd work on but it immediately make some of that stuff more clear. One of the goal or constraints is to really try and break down the silos. Whatever I'm about to propose bringing to Ember, I want it also be something that would be useful, possibly at the component or template or controller level, rather than just being this thing that lives only in the router's weird black box of logic that occasionally calls hooks that everyone knows about.

CHARLES: Right. In a sense, I'd say that they both suffer from that same problem. I'm curious to hear about the firehose.

ALEX: To actually get into what I think you're building here, we can dance around it all day and then we --

CHARLES: Just save it for the last 30 seconds of the podcast. That way there could be no --

ALEX: We're swapping JS for React router V4. Bye! It’s basically this. What's happening today is that you have a URL, it's going to be parsed in a way that you've tied it to via the router map file, which every Ember app has the place to go to see all the different places that you can navigate to an Ember app, which is great. You basically taught Ember how to break your long URL string into these usable bits and that's going to give you an array of these things that internally who cares what they're called but they're called handler infos and they basically say, "The first element of this array is named application. Every Ember app has one. It doesn't have any params."

The next one, it starts getting into what your URL actually is. Maybe it corresponds to the '/post' portion of the URL so that's going to be named 'post,' and that doesn't have any extra params either. Then there's this thing that is post show or something like that. That has a dynamic param because that's the part of the URL as like the '/123' and that corresponds to the post ID. It's basically, if you like thinking of things in terms of transformations or observables or mapping and functional transformations, that's taking a URL and turning it into an array of these useful POJOs of information. The goal is to keep transforming that into something eventually has enough data to display and templates and whatnot.

In this giant black box of the Ember router, it's going through those transformations and then it's going to go through this long series of using these params and this useful array of POJO information, start hitting hooks on people's routes to load data. Hit before model after model, redirect all these things to give tasteful names to all the tons of validations and checks that you might want to do. You do cool things in your before model hooks, check if the current user is actually an admin to prevent them from going into any '/admin' subroute. That's a really cool place to go and it's also a great convention.

If you're new in Ember app, you realize you can't go on this route. It should sort of click in your head and that sounds like they've got one of these redirect hooks to ensure that you're not going anywhere you're not supposed to go. All these things are really still to this day, extremely strong, well-designed, it went through many passes of review before it landed. I think they cater to a certain kinds of user-driven clicking around apps but they are extremely strong to this day.

I think the only thing that's missing is the smell. That example I gave like checking if the user is an admin, it's a bit of a smell that is not reactive. It's a hook. If it passes, great. You're in the route. It's not going to keep on checking that. What I want to do is basically, either in addition to or as an alternative to specifying these one-off model hooks or these hooks that you, not only really just fire one time, have essentially what is an async computed property or an async validation that is upfront about things it depends on.

Ember is going to be smart enough to constantly reevaluate these things as stuff changes. It can depend on not just URLs or URL parameters but it can also depend on data. If you're thinking about ember-rideshare, which again is the imaginary Ember app that it's essentially Lyft or Uber, if you have a current ride model loaded somewhere, maybe by a parent route or maybe it's some sort of service, you should be able to specify it like an async property or validation that says, "I depend on ride.state," and for all these subroutes, you would want to say that, either upon entry or any point in the future, if the state ever changes to something that I don't know how to handle that go to some default route.

That would be already, particularly in my app, which is a subset of a different kind of ember-rideshare app, that would be a huge help because the only other alternative is to build a sibling-central coordinator to the router that isn't the router but has to sort of agree with it and then, every one of these frames that you might push onto the navigation stack, they have to do some little chunk of code and then invoke this logic and be like, "Did the state change? Go where you're supposed to go," and they have to do that logic.

It would be, I think a great win for conventions as it has if it's a benefit to make people shout out their states in advance to empower them to shout out also their data constraints in advance so that you get things like automatic redirects and things change, I think that would be huge. I know that would immediately benefit off of it and I think it would fall in the same kind of problem solving that they worked on like Ember-related stuff which people don't realize how big a problem is until they see there's a better way of doing stuff. I think with that being there --

CHARLES: As an example, let's say that you're an admin and then all of a sudden, you got fired and there's an event that comes from a server that's this person is no longer an admin and it wipes out the Ember data store and then redirect you outside of the admin route or something like that.

ALEX: Yeah, that's a perfect example. To be pedantic, I think a lot of people do hard refreshes between login/sign-off stuff but if you have it all in your Ember app, that would just happen automatically. You'd still want the ability to have more graceful transitions because one of the tricky things about having stuff driven by data is that you have this giant matrix of like, "If I'm in this state and this event happens, how do I handle it? How do I make it look well-designed to the user?" But you're not going to be able to hit every one of those constraints so to just have some basic logic that's just like, "Oops, something happened," you're not an admin so we move you to the sign-in page. For in those cases, we haven't fully filled in all those leaks. I think it would be a huge win and you can just progressively decorate things according to the common flows that people take through your app.

CHARLES: You know, I'm just imagining this. Model promise, for example would be some computed property, then how would you enumerate your dependencies? Just do the mechanism that we have now? Or are you imagining something entirely new?

ALEX: I don't have a strong opinion on it because the moment I start saying what that specific syntax is, more people will agree on what's missing and what we need to have, regardless and be like, "I don't like it." I'm leaning toward something inspired by a lot of my learnings from observables, which is actually we talked about last time. The whole thing about observables is that there's almost limitless flexibility as to if you're in observable, it can take that event. It has been another observable based on that thing.

If a URL changes and you're listening to that via observable description, inside that, you could kick off another observable of Ajax request based on that URL and it doesn't make you enumerate all these things upfront. I think there is going to be a compromise between that. I think when you get into these kinds of problems, you run into stuff like Relay, which is familiar with --

CHARLES: I haven't used Relay.

ALEX: Just the idea of dynamically collecting all of your dependencies upfront before hitting the server and asking for specific chunks of data that you need, it's a very promising idea. There's cases of just dynamicism where the data comes back from the server, then you realized that you need this other piece of data and there's no way you could have collected upfront, unless you statically wrote it upfront. I expect to find that with this approach that there's going to be some stuff where you just have to be more upfront about it. But I had a cool little strike the other day on auto-computed properties and I'll also link to that. It's a different way of running computer properties where you don't have to specify your depending keys upfront but your getter function gets passed a getter function itself.

CHARLES: It's past the dependencies?

ALEX: Not even that. Imagine writing a computer property and the first [inaudible] is a function that you can call to get a property off of this but also track that you've got that property. If it ever changes, it'll invalidate again. That means if you're implementing a [inaudible] in computer property, you don't have to write first name twice, both in your dependent keys and in the actual getter in your function, which I think is kind of cool. I'm trying to make that pattern work for this data loading thing so that you don't have to have this huge verbose thing. You just lift this stuff in one place. I've sensed that the magic will probably break down in some complicated cases but that's what I'm trying to run with because I think it's pretty cool and succinct and sort of the natural evolution of what people think of as computer properties.

The other major constraint and this is also what we're talking about because it's one of the best kept secrets about the router or it's one of these things that everyone's benefiting from without realizing it, is that if a transition occurs in the router, everything in the router is going to be a possibly long asynchronous chain of operations that it collects all the data that it needs for the new routes to display. In that time, if something happens, if some hook comes along and has an exception, it can load data from the servers. If something happens then it just says 'transition.abort,' that's going to stop whatever transition is in place and you're going to stay exactly where you were and if you're not stuck in a partial transition state, that's pretty awesome. That's basically database atomic transaction semantics that people have been benefiting from if they've been using Ember for years at this point.

But again, it suffers a problem being locked away in the router. That is a cool concept. You should be able to specify like I intend this change of the state this way and if I gave you something that is logically inconsistent or can't be fulfilled, don't leave me in a weird half-assed state that I need to somehow fix and know how to fix all the different places, where I might be kicking off this transaction. I'm trying desperately to preserve those semantics when data comes into it.

One of the hardest things to do is and honestly, can be one of the hardest sells for people who are used to thinking about Ember is there's an issue of if you imagine whatever API we're talking about, it's probably going to live on the route. Some kind of hook that might be called resolve or something else, like what is the value of this context object that every function has? Is it a route? It’s tempting to want to do that and maybe, that will end up winning but winning out is the best API to get people to use.

The thing to realize is that there is no consistent value of this. This implies that there's a state of the world and you're looking at it and currently, these things have these values. But in the transaction phase, there is no stable 'this object' and you can wind up with some weird surprises. I know because, not actually these days but particularly, when a lot of the stuff landed and people started trying to do weird things and these transaction hooks, there's just like, "Why can't I grab the controller? The property isn't what I expected?" Honestly, all the stuff that is gross about query params because of this fundamental violation. You have something that pretends to be a property that is there today but is still driving this asynchronous thing that could fail.

CHARLES: I kind of viewed this as playing an off-note in the jazz thing like you only want to reserve using this, unless you're the Miles Davis of JavaScript, don't use this.

ALEX: And by Miles Davis, you just mean like the god of concurrency that's incorrect race-condition-y code.

CHARLES: Right, so it's just like you've got the right reason and you can spot the one-in-a-million case, where it's appropriate. You can spot it in an instant.

ALEX: Exactly. I'm not that person and I don't know too many people who are and that's not the API you want to land. I'm trying to, maybe wean people off on dependency on this because the way we've gotten around it in the past is to use again, is more discrete, get the value functions called 'get model' and 'get params.' These are all very in-depth stuff if you're pretty experience Ember developer but it's a way of getting a value from one of these parent routes when you're inside a transition and the rest the world can't see it but you can because you call this hook at the right time.

It's super gross because it's just a method on a route that anyone can call in any given time, whether you're inside this transaction or not. The branching logic of, "Should I look up the data from the transaction object?" because once valid, I should have get the current value of a loaded route. It's really gross to me and it causes real problems that confuse people and causes them to write issues because they've given an API that makes them feel good about treating these things as stable objects.

CHARLES: I'm trying to imagine now, just like a spike in my head. I know you don't want to get too into syntax but essentially, modeling the route tree as a set of observables, where essentially, instead of returning a promise from your model, you're just mapping an observable off of some combination of the URL state or what are the other streams of state you want to merge to realize that route. But what I'm not seeing, which I'm sure you also have the answer is the original problem, which was stack routing. What we've been talking about is making the router fully reactive like this fully reactive tree that's always on. But that problem seems almost orthogonal to the stock routing problem.

ALEX: It is. It's been very tempting to combine them. Why it is such a hard problem? Because you've got navigation stack, which almost to this route hierarchy stack that [inaudible] about but they're separate so you can't really apply the same lessons. Then you've got stack routing, which is you want the ability for routes to while they're loading, reference data that is dynamically available to them. I don't have a solid answer but I would say, the one thing that I think is going to help is that you have a few options for what you want to stash how you want to represent a URL or where you want to stash your hierarchy. Actually just track it in-memory and if you refresh the page, it'd be like, "I depend on some data that I expected to be there but it's not. It transition elsewhere," which is not a great developer experience. You could want to be able to make changes and refresh the page and continue where you left off. Otherwise, URLs aren't actually used by mobile app users.

But the other place that you could possibly put the navigation where event stack is in a query param because that can be fully dynamic and you can just sort of manage every single page. The most current page you've pop is just some top-level route but you're tracking the state on the side. I think if you solve the problem of being able to depend on things that aren't the URL or go through a more complex transition than what the router gives you by default, I think it would be possible to treat that query param or that thing you're stashing in in-memory as another source of data.

The other thing that I want to try and make sure that this new API has is really treated dependency injection where you specify all the things that you need and you don't really care from a route's perspective where they come from. I think if you had that, that would solve a lot of problems with stack routing and where it gets data from. To be very specific, today if you were in that post '1, 2, 3' comments route and you needed to access the post model from within the comments route, you would probably do this model for post.

Basically you're naming not just the model that you need. You're naming the route that you know provides it upfront, which I think is that. Actually, the real reason it's kind of the smell is that, if you ever need to change the nesting, maybe you need to introduce another level or you want to nest all that under an admin route. Then suddenly, you're asking for the wrong route name. You're not really sure all the different things you need to update if you ever change the nesting of your router. There's solutions like relative URLs that a lot of people thrown around but I think --

CHARLES: To go back in the observable world and specifically, the redux-observable world, it's like a simple map. You're just mapping down off of a global prop, you've got some tree of state and you're just mapping off... What was that like? A model hook and you're just mapping down off of that? Wherever that state lives, you're mapping to it and now you kind of slicing off your little garden hose off of the firehose. But still one huge --

ALEX: I've tried to apply observables to this problem. I don't think I've never seen the observable analogue of is this idea of dependency and injection. To model something as a stream that transforms over time, that's proven to be very useful but to sort of say, "I am an observable that expects these objects given to me," I'm not really sure what that API would look.

CHARLES: I would say, just as a straw man perhaps, you have this dependency that it's a well-known location. It's a well-known name. With dependency [inaudible] in classic, it's like, "I depend on the off service. This thing called 'service:off' or whatever. Imagine that you have some pool of state and there's some key called ‘service.off’ there and as long as I'm just basically basing my stream, the first thing I do is map off of this and maybe map off of another key and then combined those into a single stream, then I can be sure that I have those things at all times. If they change, my mapping function or my transformation function is going to get evaluated again. Does that make sense?

ALEX: Yes, I think we should [inaudible] C without code or something.

CHARLES: And maybe I'm thinking about it wrongheadedly but that would be a simple mechanism.

ALEX: Could you run by me one more time --?

CHARLES: Yeah. Let's say that we've got some authentication service that you want to depend on like you want to inject on it. You want to inject that dependency so why can't you base your stream off of that key? You have observable map, for example. The list of transformations that you would have to do to peel off multiple keys, I'm sure you could write helpers for it. But basically, probably if you're going to be wanting to inject multiple dependencies will --

ALEX: The problem is this. Basically, if you want to write your resolved observable, if this thing based on observables, remember that there is no this in a route because of the transactional reasons of what we've talked about earlier, what are you getting that from? You need to have something passed into you, to be like 'context.get observable blah.'

CHARLES: I would just assume that it's implicit. I was thinking a bit basically, the simplest case would just be an observable that was basically taken off of the entire global state or whatever of the router or what have you. The way the redux-observable works is every single epic is what they call them is just a transformation on the global stream. Usually, the first thing that happens is they map down to the local context so the --

ALEX: Like a path?

CHARLES: They have a helper like action of type, blah. You only see a subset of the actions that get maps to the Redux store. I think it's redux independent but at least in theory, every single epic is basically going off of the entire global state but the first in reality, what the first thing that happens is you're like, "I am only interested in this subset of the state," so you do a map off of the global state down to your local scope and then you work from there. In fact if you had the convention around that, you could even make that part implicit. It's like I return an observable that it's only seeing the stream of local states.

ALEX: That makes sense if there's sort of canonical state of the world but what you're doing when you're transitioning into a route is trying to feel out another state in an asynchronous manner. Redux is the action causes state to change, now the state is this. But the action for type thing, I think that makes sense if you are subscribing to the world global action on this one store when you're constructing this new tentative, may not actually become the store, you're depending on values. What we need in our API is something that depends on values that are from a tentative store.

CHARLES: It's similar so in redux-observable, you're mapping actions to actions and you're not necessarily mapping actions here. You want to get state into the equation.

ALEX: Yeah and it's so almost observables. It's just this twist of transaction dependency injection. It sounds really over-engineered but the thing is it exists in Ember today and if it exists in a less siloed way, I would certainly benefit on it. I think everyone else would too.

CHARLES: Okay. With that hand wave...

ALEX: Oh, I didn't mean for that to come as a hand wave.

CHARLES: No, no, no. I'm kidding because I think we actually have a lot more to talk about here and we're running out of time. One of the thing that I want to ask is, talking about redux-observable, talking about redux and stuff, have you given any thought as to what this might look as a library that everybody could use?

ALEX: I basically have something that's using Ember CLI only because it's so easy to just use it as a sketch pad and get test passing but everything I'm building so far is just ES6 class syntax that can be transpiled in it to whatever. I'm actually realizing, there's a lot of overlap between some of the primitives that are involved and Glimmer so it may or may not have a pass that uses references for tracking when things change until no one to invalidate and refire these async hooks. But either way, I'm going to make sure it lives in the JS usable world and not just Ember's special object model end.

CHARLES: Right. Those interfaces are pretty narrow. The things that implement those interfaces are huge and complex but the way, at least I understand it, isn't the reference interfaces themselves --

ALEX: They're really simple, yeah.

CHARLES: -- Really simple. It could almost be copied and pasted and not have much maintenance overhead in there. Here's a question and this is probably getting too far into the weeds. Can you not model a transaction as an observable? Essentially, with a flatMap, you would merge in some observable into the chain that was basically a transaction of all the other observables from which it is composed.

ALEX: You know, a transaction as it builds up all the new state over time could be part of the main tree and if there is an active transition, then that's future potential state that the world might become and it could be modeled as a leg of the Redux state. I think you could theoretically do that. Definitely worth a try. I don't think I would benefit too much from doing it now and I think this could be a premature optimization but I think there would be just quite a bit of intermediate object collection to express that. I think theoretically it works but how it's going to physically map to Ember in the near future, it would be harder [inaudible] in a way.

There's actually a lot of stuff that is very redux-y that again, a lot of Ember people don't maybe know about because it's internal but the way that Ember [inaudible], I think since Edward brought some of his learnings of Liquid Fire back to core Ember, there's this concept of outlet state, which describes -- I'm not an expert on it -- what's rendered where and then each outlet gets a chunk. Like you said, a little piece of the firehose or garden hose, pulled off the main thing so it can just focus on the one piece of state. Those are simple objects that produce this part of this transformation process. That's kind of redux-y in the way that everything just gets a new POJO and stuff changes but it's not strictly redux, obviously and probably won't become that just because it's already good enough on its own.

CHARLES: Yeah. I think it's actually good at this point to be hand wavy because the most important thing is to be non-committal about the syntax, like you said because that's when the bikeshedding begins and now it's not the phase. The phase is to come to some agreement about what is that we would love to see.

ALEX: Basically, the thing is this. I think people need to realize that Ember won the bet that the URL is an important thing to build apps around and if you have a state that's representable in URL, that state should go in the URL so you can send links around and not break the web and have an app that works that's built on half-assed routing. The only thing I'm proposing is going to make that go away. It's just that there is already this giant world of stuff that's not expressible in Ember today because it is driven by state. If you make that as easy to express and as upfront to express, I think you can have shared conventions versus what everyone is building these apps that I have to do, which is to make a sort of separate router of state-aware stuff and not have to make those two things agree with each other because it's really hard.

CHARLES: Right. At that point, you're writing your own framework. Maybe this is the next big thing because I feel like Ember usually has the best stuff way, way, way, way before. Now, we're finally getting to a point where everybody seems to realize that having a CLI is absolutely critical to the developer's experience and most frameworks aren't taken seriously until they've achieved that. It was the same thing with a router back in the day. I'm wondering what that next thing is.

ALEX: I don't know. I don't think this is going to be it. I just think it's a good progression. I think a way forward that progress is still a pretty legit central structure to build apps around and just would be welcomed.

CHARLES: When are you going to be done?

ALEX: About two or three days. I don't know. I think I'm basically going to be continuing to get feedback like the way that a lot of that original router stuff came back or it's just like constantly hit people with real examples, Ember twiddles, things are just like, "Oh, yeah. That thing. That's a cool pattern. That sucks in my app. I didn't realize that until I saw this example." These things that really teach people why this is necessary because that's going to get people's urge to be like, "Well, you could just do..." Oh, you can't because the thing that's hard to explain. It's going to be a lot of that regardless and I hope that will kick off in the next few weeks.

CHARLES: And the focus of that is going to be the ember-rideshare application.

ALEX: I think that's a good one. This is one that everyone's familiar with.

CHARLES: Have you already kind of implemented in it, like this kind of Frankenstein-ish, like this is the kind of histrionics that you have to go through in order to implement the style of routing or the style of application using today's Ember? Or have you started to begin experimentation with these new concepts and try to build out better ways of doing it?

ALEX: I'm not strictly extracting it from one app. It's sort of combined. Like I said, the few different apps that we had were an opportunity to be like, "This sporadic stuff is hard." The main route recognizer approach was an example to try different stack routing pattern. But the thing that sort of working on is drawing from three different apps and slightly different takes on it. Basically, I have something that is close to being testable in one of my main apps that will be a great chance to validate if all the stuff is as nice as I think it is going to be.

CHARLES: Okay. If the people want to get in touch with you, to help to contribute to the conversation or just publicly guilt you into moving faster towards it, how would they get in touch with you?

ALEX: I'm at @Machty on Twitter and GitHub and also, the Ember community Slack. I think I'm going to try to get people to talk about this on channel called Dev Dx Router where it's focused on development stuff all around the router. This is kind of funny because I'm talking about this thing that I've only had maybe, 12 people take a look at and comment on and begins these conversations. I think maybe some people are going to hear this and be like, "What are you talking about?" but if it gets people --

CHARLES: No, no, no. You know, the best conversations seemed to be organized around you, man. I'm just trying to think of some of the best development conversations that I've had in 2017 and you were definitely, I would say the one who fomented them. It starts with 12 people but then, if enough people take interest and be like, "Wow, yeah. Oh, man. I didn't even know that was a problem. This would be a cool way of doing it." They have a tendency to balloon and some fizzle out and some end up with real results. Anyway, I'm looking forward to it.

ALEX: I appreciate it and likewise, you're definitely one of the best people to talk about this stuff with.

CHARLES: Well, I hope other people will love listening to our conversation. With that, we'll head on out. Thank you everybody if you've made it this far. As always, you can get in touch with us at @TheFrontside on Twitter or just send an email to Contact@Frontside.io. We will talk to you next week.

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