What does the Magento_Ui/js/lib/knockout/extender/bound-nodes RequireJS Module Do?

Question

The Knockout.js bootstrap module in Magento 2 includes the following module via a define dependency.

 Magento_Ui/js/lib/knockout/extender/bound-nodes

Technically speaking, this module creates wrappers for the ko.applyBindings and ko.cleanNode methods. These wrappers will stash certain view models and nodes in a private javascript WeakMap, and then return a single registry object that will let you access items in the WeakMap.

However, it's not clear what end-user-programmer facing features this enables. Does anyone here know what the Magento_Ui/js/lib/knockout/extender/bound-nodes module is actually for? Or is familiar enough with Knockout.js internals to figure things out?

Answer 1

The Magento_Ui/js/lib/knockout/extender/bound-nodes registry will, theoretically, let you fetch a list of HTML-DOM nodes that are scopeded to a particular view model. i.e. you should be able to say something like this

boundNodes = requirejs('Magento_Ui/js/lib/knockout/extender/bound-nodes');
reg = requirejs('uiRegistry');    
viewModel = reg.get('customer');
console.log( boundNodes.get(viewModel) );

and get back a reference to the li node that's scoped with customer

<li class="greet welcome" data-bind="scope: 'customer'">
    <!-- ko if: customer().fullname  -->
    <span data-bind="text: new String('Welcome, %1!').replace('%1', customer().firstname)">
    </span>
    <!-- /ko -->
    <!-- ko ifnot: customer().fullname  -->
    <span data-bind="html:'Default welcome msg!'"></span>
    <!-- /ko -->
</li>

You'll notice the use of theoretically and should. The problem, per this community forum thread, is there's been an undiscovered bug in the Magento_Ui/js/lib/knockout/extender/bound-nodes module lurking for a while now. It is not, as of the 2.1.x branch, code you can rely on.