June 21, 2015

Difficulty Of Managing A Single Bit // AmpersandJS

the what.

AmpersandJS forms. Amazing little constructs. But to make them render reliably and consistently--it was a battle! One particular bit, indicating their rendered state, proved to be much more complicated than anticipated.

forms. give me simple forms.

Let's talk context. @MRN, we do a lot of assessessments. What's an assessment. An assessment is a glorified term for research survey, in nuero-speak. What do surveys need? Forms. @Henrik Joreteg's blurb on web forms is one of the most refreshing short bits declaring how forms should really behave. When I first read it, I was very curious to see if the hype was true. Consider my prior strategies managing form data:

// does this look familiar?
var form = service.getMyOldFormValues();  
var $input = jQuery('#sillyInput');  
if (form.input.init !== undefined) $input.val(form.input.init);

// inside some change handler...
if ($input.val() === 'bananas') {  
    console.warn('how many huge, redundant condition blocks like me will a complicated form have?');
}

// what's tight about this?  i get my data in one place, i initialize my control in another, i validate in a third, and hopefully i've got some standard notification mechanism for validation messages and submissions.  abort!

ampersand takes a modern approach:

This is a drastic improvement over our existing form handling strategies. Why. Because we've decoupled ourselves from the formal <form> behaviors, and used the form for it's original purpose--get data from the user, not to get-the-data-that-may-or-may-not-be-in-the-format-we-need and to immediately submit said data to some remote page. <form> has lots of sugar to make forms work in a fashion that were helpful when we did all of our web application work on the server. That time is gone.

forms. give me a consistent interface for all of my fields.

The API's for many of these &-js form-fields were slightly inconsistent. The docs? They all had a good start, but were still lacked key details. For example, between a couple of FieldViews, you may not be sure the fate of an el that you provided to the field. Would the FieldView

It was challenging. There were more than a couple bugs. In the beginning, I just needed to get my app to work, so I started tossing in patches n' bugfixes. More than just bugfixes, however, we wanted a consistent interface to enable the form itself to perform operations on its member fields. This has been mostly completed via form-view initiatives.

forms. assessments. are we good to go?

So what does this have to do with the managing a single bit? Again, @MRN, users consuming our product, COINS, fill out a variety of complex forms, often with custom in-house designed controls (cool!). Form management is our business. Trouble is, the system is huge and it's all written using a flat, procedural, global-esqe data paradigm. Surveys are built server-side with logic, DOM templates, and data embedded into {js-objects} which in turn encoded into the resultant HTML fetched from the server. It's made up-keep a bit tricky.

seperate the survey's concerns

Ok, let's replace the form templates from the server with more flexible ampersand-form-views, and simply pipe in data to the form for it to manage. Unfortunately, the mapping isn't so clean. A survey is really a collection of forms, paginated. To address this very problem, I built and released ampersand-form-manager-view. It's a handy little library to take a series of forms, and enable you to get the state of the set of forms. That is, provide it a series of forms, and it could tell you that all forms are complete and valid, or not! This is where that single bit came to bite!

the elusive bit

The single bit under fire was the rendered boolean flag in &-view. &-form-manager-view cycles through forms. However, when cycling back to a previously viewed form... nothing would show!

This leads us to rendered definition 1: the view is rendered if it has an element. This was the state of &-view when I began. How dishonest! ;) The fault of this definition is that my views had been cycled in and out, hence removed. However, the element they were rendered into still existed! Therefore, the view still believed it was rendered! You might say "just remove the el from the view defintion" on view removal. This doesn't work because often a view will be initialized with an el, but not yet rendered on screen. In that case, rendered would report true, when indeed, all we did was initialize, not call the render() function itself.

definition 2 is that the view is never rendered. Remove rendered state from the &-view library. The rendered state of a view shouldn't be managed by &-view. Instead, let the user manage this piece of state on his/her own. This drastically cuts down on usability, and bloats &-view defintions.

definition 3 is that the rendered bit gets autoloaded into the state as a prop, and render() and remove() functions toggle the bit. When the user overrides one of these functions, a custom getter/setter wraps the user provided function with logic to set the bit.

Although some implementations of definition 3 trigger redundant events if the prototype is extended, an agreeable solution was found using session-wise and derived+cached attributes. The solution sets a session _rendered attribute to true on every call to render(). There may be many calls to various render() fns if a View definition is extended multiple times. This emits many events, but the view is really only rendering once. So, because we only want to emit one event for the user to actually act on, we exploit the fact that the derived rendered attribute only executes its value handler when the session value _rendered has changed. In this regard, only a single change:rendered event gets emitted, and we can manually trigger a matching render event at the same time, as some folks want to listen for the action vs. the state.

It was challenging to land on a solution that would honor &-view's contracts for eventing as well as pre-rendered, rendered, and post-rendered state. You can see bits and pieces in the ampersand-state source.

closing thoughts

What a rabbit hole. We visited forms, form-management and composition, jumped over to views, then finally examined how I ended up making stateful views honest! There's often a story behind each PR. This was the story behind mine.

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