Refactor out reference to IPython.* reference away from behaviors and replace them with Urth.*

[lbustelo]

In various behaviors we got references to IPython global. Due to potential inconsistencies based on the environment that the notebook code is running (i.e. dashboards), we need a more reliable (injectable) way to set these dependencies.

I suggest that we isolate that into our nb-extension/js/init/init.js and allow it to be injected by the app code.

Most of the code that reference IPython should be under elements/urth-core-behaviors

[jhpedemonte]

Here's the code we currently use on dashboards server to shim declwidgets: https://github.com/jupyter-incubator/dashboards_server/blob/c7909c79ae21930334d78a39dac21d71b192fa52/public/js/widget-manager.js#L177-L208. There are two sections: the first is only called once, on initialization; the latter is called per cell, on execution of code.

The first section (_shimDeclWidgets) sets up a lot of the IPython globals. It makes use of the kernel instance (from jupyter-js-services) and sets the widget_manager property. If we pass in the WidgetManager instance as suggested by #196, the code could also get the kernel instace. But not sure how "correct" that is.

The second sections (_hookupDeclWidgetsCallbacks) is a bit more complicated and much more tailored to the latest jupyter-js-widgets code. Also, the "callbacks" situation has changed (see jupyter-widgets/ipywidgets@c56b85b) -- that code was moved out of the generic ManagerBase and moved to the notebook-specific WidgetManager class. Plus, you'll need to somehow set this up during code execution -- maybe we'll need an API/callback on widget manager?

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To start off with, I think the declwidgets init code could do a simple check to see if it's running in the notebook or not:

if (!window.IPython || !window.IPython.notebook) {
    // not in Notebook, setup shims
}

init() could take an optional widget manager instance in order to setup the shims.

My branch with declwidgets changes is here: master...jhpedemonte:StandaloneExperiment and contains some necessary changes to work with latest code (hopefully also backwards compatible):

• I don't think the change to nb-extension/js/init/init.js is necessary.
• The change to DeclWidgetModel.js is fairly straight forward, just a new way of extending the base WidgetModel class so it works with other changes they made in the code.
• The change to jupyter-widget-behavior.html is interesting. They changed the API to new_widget -- not sure if you can pass the empty object and have it work with both old notebook code and the newer jupyter-js-widgets code.

cc @deedubbu @parente

[purdrew]

Commit 1085b21 now uses dependency injection for the Jupyter definition. However, the code is still assuming certain things to be in that Jupyter object (ie. Jupyter.notebook.kernel, Jupyter.notebook.base_url). @lbustelo Do you think the code changes in 1085b21 is sufficient to close this item?

[lbustelo]

I think so.