[WIP] Changes necessary to work standalone similar to ipywidgets examples

[lbustelo]

This PR is just intended as an experiment of what it would take for declarativewidgets to operate in a standalone jupyter-js-services.

I'm following https://github.com/ipython/ipywidgets/tree/9602b80f627656171cbda55ddb92481146325920/examples/development/web3 as a template.

[parente]

We should also compare notes with jupyter/dashboards#127 which is out of date but still has the bulk of the code for using jupyter-js-services instead of Thebe. Also, https://github.com/jupyter-incubator/dashboards_nodejs_app which will be the default ref impl for "give me this notebook as a securable app".

[lbustelo]

A couple of the challenges in this work:

1. Converting our project into an npm module. Easily started with an index.js but the challenge is what to export. For now I'm just exporting the init function.
2. The extension js code needs to be altered to support loading as npm package and also on the browser. The demo is using browserify to build the js code.
3. Where is IPython global? Not that it has to be named that, but were do we find the equivalent dependencies.
4. WidgetManager vs ManagerBase
5. bower_components vs urth_components. Had to temporary create a sym link to move along
6. A require shim is needed to define declare and adjust module loading paths as necessary.

[lbustelo]

So basically was able to get through the bootstrap stage of setting up the page with declarativewidgets support. Had to make some changes to prevent undefined access and shim several things on the IPython global.

This demo shows the following:

1. Bootstrapping of the APP working
2. A template on the DOM using urth-core-bind directly on the HTML. No need for magic (a la %%HTML).
3. Code sent to the kernel to set a variable on the channel
4. The template responding to that variable change and rendering the message.
   

[lbustelo]

Latest commit modifies the example to use urth-core-function' as well as shimming the 'shell_reply.Kernel event.

[parente]

/cc @dalogsdon @jhpedemonte since you're paving the way for everything that needs to go into jupyter/dashboards_server#2

[jhpedemonte]

que?

[jhpedemonte]

jupyter-widgets/ipywidgets#383 made a change to WidgetModel which breaks DeclWidgetModel. Specifically, it made _deserialize_state() a "class" level function which is not carried over into DeclWidgetModel when that extends WidgetModel.

I thought of adding generic code such as this:

for (var key in Widgets.WidgetModel) {
    if (Widgets.WidgetModel.hasOwnProperty(key))
        DeclWidgetModel[key] = Widgets.WidgetModel[key]
}

Unfortunately, in addition to _deserialize_state, this would also add extend and __super__ (Backbone related?).

We could just directly map _deserialize_state, but that's fragile. Another option is to make use of the WidgetModel.extend in order to create DeclWidgetModel -- not sure if that will bring over "class" method.

Also, I don't like that we need to bring over a "private" (starts with underscore) method in order to extend WidgetModel. I'll open an issue with ipywidgets.

[jhpedemonte]

Another option is to make use of the WidgetModel.extend in order to create DeclWidgetModel

This works.

[jhpedemonte]

Another issue: new_widget() now expects a serialized_state as 2nd argument. I'm currently failing on JupyterWidgetBehavior._doCreateModel(), which only passes in an options arg. @lbustelo, any ideas on how best to fix that? I'll keep investigating.

[lbustelo]

I'm closing this PR since @jhpedemonte has already made the necessary changes in #251