Form controller in marionette - backbone.js

Question

So I have a form that appears on a few pages and contains a number of groups of inputs. Say group a, group b and group c. On some pages they might have a and b and on others the form contains b and c. Each group may require its own client side custom validation maybe executed from the form controller.
What is the best way to achieve this using backbone and marionette?
Conceptually, and i'm fairly new to both, I'd assume I'd need a FormController that is instantiated from a page specific Controller which also instantiates the group controllers that I need for that page. Any advice would be great.

Answer 1

TL;DR
To make this work you would create two objects per input group. One for its custom functions, and one for its events. In the form controller you'd _.extend the function objects of each input group with a base form view to get the custom functions into your new form view. Next you'd pass in your custom events objects into the constructor for the new form view, where a utility function of your basic view would add the new custom events to the basic form view events. Finally, you'd have to ensure that you have a template for that form that contains the correct input groups.
I should also mention that you can accomplish this with Marionette.LayoutViews and dynamic regions, in a possibly cleaner way (you could specify an atomic template for each input group), albeit with a lot more overhead.
The expanded explanation
I've been toying with this idea a bit. I've been thinking a lot lately about using Underscore _.extend() to plug-in stock functionality to different views. Your problem would be ideal for this solution. Here's a sample of how you'd implement it.
Including functionality
Say that your input group A had a validate function that did it's thing,
validateA: function () {
// custom validation routine
},
and a submit function to handle form submissions,
submitA: function () {
// custom submit routine
}
The first thing you do is package these functions inside an object:
groupA = {
validateA: function() {...},
submitA: function() {...}
}
You'd have as many function objects as you have input groups.
You'd also build a generic form view that would house common form functionality, and which would also serve as the basic view you'd use to render your form
var GenericForm = Backbone.Marionette.ItemView.extend({...});
In here you'll put all your baseline events and functions common to all forms.
Then, as you mentioned you'd set up a FormController that would plug in the custom functionality, like this,
var formController = function () {
callFormZ: function() {
var genericForm = new GenericForm({ groupEvents: [eventsA, eventsB] });
var formZ = _.extend(genericForm, groupA, groupB);
SomeRegion.show(formZ);
}
}
By using _.extend on your basic view and your two input groups you end up with a new view, formZ that is a composite of the two input groups. If you'd look inside it would have all the functionality of GenericForm plus
{
validateA: function () { ... },
submitA: function () { ... },
validateB: function () { ... },
submitB: function () { ... },
}
Events
At this point, though there is no way to bind any events to your custom functions.
You may have noticed in the callFormZ controller that I passed in an array in a property called groupEvents. These are the custom events for your input groups. They'd normally have the form
eventsA: {
'blur .groupA': 'validateA',
'click #groupA button': 'submitA'
}
Ideally, we would just use extend to merge your events the way we did your functions. But since we want to end up with just one events property in your view, we run into a problem. _.extend will overwrite all the events properties in your view object with the events property of the last object passed into _.extend. So to get around this problem we have to pass an array of custom events, one for each form group.
First, you'd create a config array of events objects with your custom events for the particular form you're working with,
customEvents = [
eventsA: {
'blur .groupA': 'validateA',
'click #groupA button': 'submitA'
},
eventsB: {
'blur .groupB': 'validateB',
'click #groupB button': 'submitBA'
}];
You'd pass this array into your constructor, as we did in the callFormZ controller function. The array will now be loaded in your options parameter. In your initialize you can call something like this,
initialize(options) {
combineEvents(options.groupEvents);
this.delegateEvents();
}
where, combinedEvents is
combineEvents: function() {
var extendEvents = [this.eventsA, this.eventB]; // Make an array of the extended groups
_.each(extendEvents, function (extendEvent) {
for (prop in extendEvent)
this.event[prop] = extendEvent[prop];
}
}
Also, note that after combining events I called delegateEvents so that we'd rewire the new events.
Templates
To make all this work you'll have to provide a template that has the portions of each input group. I'm not aware of how we construct the template programmatically from individual input group templates. Instead, you'd have to have a template with the input groups relevant to the form.
Putting it all together
So, to make this work you would create two objects per input group. One for its custom functions, and one for its events. In the form controller you'd _.extend the function objects of each input group with a base form view to get the custom functions into your new form view. Next you'd pass in your custom events objects into the constructor for the new form view, where a utility function of your basic view would add the new custom events to the basic form view events. Finally, you'd have to ensure that you have a template for that form that contains the correct input groups.