Funding Gates

Thoughts on Moving Ember.js Forward

by Jo Liss (@jo_liss)

In this post, I’ll talk about the technical challenges we’ve encountered as we’ve used Ember for a medium-sized project, as compared to the smaller apps I’d written before.

The target audience is other developers that are interested in moving the Ember.js project forward. The post is mostly intended as a conversation starter. My hope is that through discussion and code, we will be in a better place a few months from now.

Note 1: If you are just trying to decide on a framework for your app, then after our experiences, I can wholeheartedly recommend Ember. I’ll blog about framework choices some other time. In the meantime, check out Peter’s talk.

Note 2: I believe that the problems I describe tend to arise with other frameworks, like Angular or Backbone, as well. (Backbone in particular doesn’t even try to address many of these things.) If you have seen or come up with solutions for other frameworks, please share them!

1. Debugging and Inspectability

This is a surprising issue, so I’ll start with this one.

Ember has great top-down documentation. However, as my team-mates dove into our Ember app, one complaint was this: The documentation gives simple, self-contained examples. Dropping from president.get('fullName') into a fully-featured Ember app is pretty brutal. It’s very hard to know what’s actually going on.

Unfortunately, Ember doesn’t make it very easy to inspect app state (check out this gist for a demonstration).

I think we need several pieces to solve this puzzle:

  • Integration with Web Inspector and Firebug: When showing Ember objects, Firebug exposes the type (through toString), but not the properties. Chrome doesn’t even show the type – just a generic ▶ Class.

    I’m guessing that we’ll need a “list all properties” function. Ember should already have all the necessary infrastructure for this (Ember.meta, etc.). Secondly, I wonder if we should link up with the Web Inspector and Firebug folks to see if there’s a way we might be able to get custom UI for inspecting Ember objects.

  • I wish it was possible to click into the page to see the view hierarchy. I’m not sure how to implement this, but my pie-in-sky dream is something like Firebug’s DOM tree, except for nested Ember views instead of DOM nodes. This might be a couple notches too ambitious, but maybe a “light” version of this will go a long way.

    Apparently the Illuminations addon does something like this, just not for Ember (yet?). Thanks to @wagenet for the pointer!

2. Testing

In my smaller Ember apps, I was able to get by with Selenium, but this is too slow for more complex apps.

Client-side testing in JavaScript is the only viable option for a fast and reliable test suite, in my opinion. QUnit is old and sturdy, but I personally like Konacha (Mocha for Rails). In addition to unit tests, it allows you to run your Ember app in an iframe, and then use jQuery to click on links and inspect the DOM. This essentially gives you a very fast synchronous client-side integration test.

Ember already brings some helpful things for testing, like the FixtureAdapter in ember-data. Still, the whole setup doesn’t feel very mature to me yet. There is no pre-made testing environment set up for you, like with Rails, so instead every project ends up with their own test setup at the moment.

So where do we go from here? It seems that there are two big issues:

  • How do we reliably reset an app between tests? I’m suggesting a solution in #1318 (Application#reset), but it seems fraught with issues. I suspect that we may need to come up with a better way. Much of the complexity of this problem comes from global state, like the App.router object.

  • How do we give people a pre-made working JavaScript test setup, like Rails does for the server side? I believe that this would belong in packages like ember-rails. For instance, perhaps ember-rails could in the future generate a Konacha setup.

Test Fixtures

There is a subtle but painful issue with fixtures for JavaScript tests: As long as you are passing down raw database columns (as tends to be the case in smaller apps), you can easily define fixtures or factories on the client side.

But if many of the JSON attributes are cooked or computed, you’ll want your fixtures guaranteed to be in sync with what the server generates. We ended up defining our fixtures in Ruby, and dumping them out as JSON into a fixtures.js file, using a generator rake task. This works OK, but it doesn’t feel very clean.

I think we’re caught between a rock and a hard place here:

On the one hand, doing all computation on the client side doesn’t seem practical yet. Even if the performance is good enough, at the moment JavaScript is still too awful a platform to implement major chunks of logic. Compare for instance this Ruby method and the equivalent Ember/CoffeeScript code.

But on the other hand, if you perform computation on the server, it becomes harder to test the JavaScript in isolation. Accordingly, you end up resorting to workarounds like generated fixture definitions.

I’d love to hear how other people approach this issue.

3. DRY Model Definitions

In smaller projects you can repeat your database columns in the Ember-side model definitions. For our more complex app, we found that this doesn’t scale. We ended up going with code generation for the ember-data model definitions, generating a schema.js file using a rake task.

I really wish there was a nicer way to get DRY model definitions.

The information for the model definitions needs to come from the server, so this cannot be solved in Ember core.

In Rails’s case, the authoritative source might be the serializer classes used by active_model_serializers. Getting that information into the client is surprisingly non-trivial: You can’t dump complete model definitions at precompilation time, along the lines of App.Blog = <%= BlogSerializer.ember_definition %>;. This is because the type of each attribute is stored in the database, and during precompilation, you don’t generally have a database.

I’m not sure how this will be solved. I do think however that we need a real, DRY solution, not just more generators in ember-rails.


These are my thoughts so far. As I said, this post was intended as a conversation starter. Once we figure out how to approach some of these things, you’ll hopefully see me writing code and not just complaining idly on our blog. ;-)

Leave a comment, open an issue, or find me on the #emberjs channel.

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