Hardcoded references to templateSources.anonymousTemplate prevent a pluggable template mechanism

[karimayachi]

Hi,

After some more investigating regarding #2500 I decided to create a new TemplateSource that keeps it's stored Nodes away from the DOM. I used a WeakMap approach and this works and solves the problem mentioned in #2500.

However, I'm having a difficult time figuring out how to use or distribute this TemplateSource without having to patch Knockout itself.

It seems to me that the TemplateSource was meant to be a pluggable system, because it is documented and instructs you to implement a specific interface (with text(), data() and node() methods). This to me indicates that you should be able create a in-place-replacement for the default source.

It's being called from the nativeTemplateEngine, so the documentation mentions that you should also create a new template engine. From the comments:

knockout/src/templating/templateSources.js

Lines 23 to 24 in a7ab29c

	// Once you've implemented a templateSource, make your template engine use it by subclassing whatever template engine you were
	// using and overriding "makeTemplateSource" to return an instance of your custom template source.

Ok, no big deal. So I made a new template engine as well to use the new template source.

But this is where the problems start:
makeTemplateSource in the templateEngine is only called on retrieval. Setting the template occurs in the template-binding, with a hardcoded dependency on the build-in tempate source.

knockout/src/templating/templating.js

Line 276 in a7ab29c

new ko.templateSources.anonymousTemplate(element)['nodes'](container);

knockout/src/templating/templating.js

Lines 280 to 283 in a7ab29c

	if (templateNodes.length > 0) {
	var container = ko.utils.moveCleanedNodesToContainerElement(templateNodes); // This also removes the nodes from their current parent
	new ko.templateSources.anonymousTemplate(element)['nodes'](container);
	} else {

So, using the template-binding (and with that the foreach-binding) with a custom template source is out. Creating a altered version of the template-binding is also not an option, because it uses a couple of private functions, so you'd have to completely write a custom template binding with the same functionality, without using the private functions.

Even if this was a feasible option: the foreach-binding injects the nativeTemplateEngine back into the template-binding:

knockout/src/binding/defaultBindings/foreach.js

Line 13 in a7ab29c

return { 'foreach': modelValue, 'templateEngine': ko.nativeTemplateEngine.instance };

So, you'd be back to square one, unless you overwrite the foreach-binding as well.

I'm puzzled. Although it seems that it should be easy to create in-place-replacements for the template sources, you can't actually do so without patching Knockout.

My main question is: am I missing something? What am I doing wrong in order to just create a custom template source to use with the template-binding and the foreach-binding?

As a proof of concept I patched Knockout to have a default source that can be overwritten

    ko.templateSources.defaultSource = ko.templateSources.anonymousTemplate;
    ko.exportSymbol('templateSources.defaultSource', ko.templateSources.defaultSource);

and I've replaced the hardcoded calls to anonymousTemplate with calls to defaultSource. This works, although to really be a solution, we would also have to handle the fact that the nativeTemplateEngine uses both anonymousTemplate and domElement sources simultaneously.

Please advice......
Thanks and regards,
Karim