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JavaScript Notebook Extensions.ipynb
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Embrasing web standards

One of the main reasons we developed the current notebook as a web application is to embrace the available-everywhere web technology.

Being a pure web application using only HTML, Javascript and CSS, the Notebook can access all of the web technology improvements for free. Thus, as browsers support for different media extend, the notebook web app should be compatible without modification.

This is also true with performance of the User Interface as the speed of the Javascript VM increases.

The other advantage of using only web technology is that the code of the interface is fully accessible to the end user, and modifiable live. Even if this task is not always easy, we strive to keep our code as accessible and reusable as possible. This should allow - with minimum effort - development of small extensions that customize the behavior of the web interface.

Tampering with the Notebook app

The first tool that is available to you and that you should be aware of are browser "developer tools". The exact name of these tools is different in each browser, and might require the installation of extensions. But basically they can allow you to inspect/modify the DOM, and interact with the Javascript code that runs the frontend.

  • In Chrome and Safari, Developer tools are in the menu [Menu -> More tools -> Developer Tools]
  • In Firefox you might need to install Firebug
  • others ?

Those will be your best friends to debug and try different approaches for your extensions.

Injecting JS

using magics

The above tools can be tedious for editing long Javascipt files. Helpfully, we provide the %%javascript magic. This allows you to quickly inject Javascript into the notebook. Still, the Javascript injected this way will not survive reloading. Hence, it is a good tool for testing and refining a script.

You might see here and there people modifying CSS and injecting Javascript into notebook by reading files and publishing them into the notebook. Not only does this often break the flow of the notebook and break the re-execution of the notebook, but it also means that you need to execute those cells every time you need to update the code.

This can still be useful in some cases, like the %autosave magic that allows you to control the time between each save. But this can be replaced by a Javascript dropdown menu to select a save interval.

In [ ]:
## You can inspect the autosave code to see what it does.


To inject Javascript we provide an entry point: custom.js that allows the user to execute and load other resources into the notebook. Javascript code in custom.js will be executed when the notebook app starts and can then be used to customize almost anything in the UI and in the behavior of the notebook.

custom.js can be found in the IPython profile dir, and so you can have different UI modifications on a per-profile basis, as well as share your modfications with others.

Because we like you....

You have been provided with an pre-existing profile folder with this tutorial... Start the notebook from the root of the tutorial directory with :

$ ipython notebook --ProfileDir.location=./profile_euroscipy
but back to theory
In [ ]:
profile_dir = ! ipython locate
profile_dir = profile_dir[0]

and custom js is in

In [ ]:
import os.path
custom_js_path = os.path.join(profile_dir,'profile_default','static','custom','custom.js')
In [ ]:
#  my custom js
with open(custom_js_path) as f:
    for l in f: 
        print l,

Note that custom.js is meant to be modified by the user. When writing a script, you can define it in a separate file and add a line of configuration into custom.js that will fetch and execute the file.

Warning : even if modification of custom.js takes effect immediately after a browser refresh (except if browser cache is aggressive), creating a file in static/ directory needs a server restart.

Exercise :

  • Create a custom.js in the right location with the following content:

    alert("hello world from custom.js")
  • Restart your server and open any notebook.

  • Be greeted by custom.js

Have a look at default custom.js, to see it's contents and for more explanation.

For the quick ones :

We've seen above that you can change the autosave rate by using a magic. This is typically something I don't want to type everytime, and that I don't like to embed into my workflow and documents. (The reader doesn't care what my autosave time is), so let's build an extension that allow to do it.

Create a dropdown elemement in the toolbar (DOM IPython.toolbar.element). You will need

  • IPython.notebook.set_autosave_interval(miliseconds)
  • know that 1 min = 60 sec, and 1 sec = 1000 ms
var label = jQuery('<label/>').text('AutoScroll Limit:');
var select = jQuery('<select/>')
     //.append(jQuery('<option/>').attr('value', '2').text('2min (default)'))
     .append(jQuery('<option/>').attr('value', undefined).text('disabled'))

     // TODO:

select.change(function() {
     var val = jQuery(this).val() // val will be the value in [2]
     // TODO
     // this will be called when dropdown changes


var time_m = [1,5,10,15,30];
for (var i=0; i < time_m.length; i++) {
     var ts = time_m[i];
                                          //[2]   ____ this will be `val` on [1]  
                                          //     | 
                                          //     v 
     select.append($('<option/>').attr('value', ts).text(thr+'min'));
     // this will fill up the dropdown `select` with
     // 1 min
     // 5 min
     // 10 min
     // 10 min
     // ...

A non-interactive example first

I like my cython to be nicely highlighted

traitlets.config.cell_magic_highlight['magic_text/x-cython'] = {}
traitlets.config.cell_magic_highlight['magic_text/x-cython'].reg = [/^%%cython/]

text/x-cython is the name of a CodeMirror mode name, the magic_ prefix will just patch the mode so that the first line that contains a magic does not screw up the highlighting. regis a list or regular expression that will trigger the change of mode.

Get more docs

Sadly, you will have to read the Javascript source file (but there are lots of comments) and/or build the Javascript documentation using YUIDoc. If you have node and yui-doc installed:

$ cd ~/ipython/IPython/html/static/notebook/js/
$ yuidoc . --server
warn: (yuidoc): Failed to extract port, setting to the default :3000
info: (yuidoc): Starting YUIDoc@0.3.45 using YUI@3.9.1 with NodeJS@0.10.15
info: (yuidoc): Scanning for yuidoc.json file.
info: (yuidoc): Starting YUIDoc with the following options:
info: (yuidoc):
{ port: 3000,
  nocode: false,
  paths: [ '.' ],
  server: true,
  outdir: './out' }
info: (yuidoc): Scanning for yuidoc.json file.
info: (server): Starting server:

and browse to to get the docs

Some convenience methods

By browsing the docs you will see that we have some convenience methods that avoid re-inventing the UI everytime :

             'label'   : 'run qtconsole',
             'icon'    : 'icon-terminal', // select your icon from 
                                          // http://fortawesome.github.io/Font-Awesome/icons/
             'callback': function(){IPython.notebook.kernel.execute('%qtconsole')}
        // add more button here if needed.

with a lot of icons you can select from.

Cell Metadata

The most requested feature is generally to be able to distinguish individual cells in the notebook, or run specific actions with them. To do so, you can either use IPython.notebook.get_selected_cell(), or rely on CellToolbar. This allows you to register a set of actions and graphical elements that will be attached to individual cells.

Cell Toolbar

You can see some examples of what can be done by toggling the Cell Toolbar selector in the toolbar on top of the notebook. It provides two default presets that are Default and slideshow. Defaults allow editing the metadata attached to each cell manually.

First we define a function that takes as the first parameter an element on the DOM into which to inject UI element. The second element will be the cell with which this element will be registerd. Then we will need to register that function and give it a name.

Register a callback

In [ ]:
var CellToolbar = IPython.CellToolbar
var toggle =  function(div, cell) {
     var button_container = $(div)

     // Let's create a button that shows the current value of the metadata
     var button = $('<button/>').addClass('btn btn-mini').text(String(cell.metadata.foo));

     // On click, change the metadata value and update the button label
                 var v = cell.metadata.foo;
                 cell.metadata.foo = !v;

     // add the button to the DOM div.

 // now we register the callback under the name foo to give the
 // user the ability to use it later
 CellToolbar.register_callback('tuto.foo', toggle);

Registering a preset

This function can now be part of any preset of the CellToolBar.

In [ ]:
IPython.CellToolbar.register_preset('Tutorial 1',['tuto.foo','default.rawedit'])
IPython.CellToolbar.register_preset('Tutorial 2',['slideshow.select','tuto.foo'])

You should now have access to two presets :

  • Tutorial 1
  • Tutorial 2

And check that the buttons you defined share state when you toggle preset. Also check that the metadata of the cell is modified when you click the button, and that the saved metadata is still available on reload.


Try to wrap the all code in a file, put this file in {profile}/static/custom/&lt;a-name&gt;.js, and add


in custom.js to have this script automatically loaded in all your notebooks.

require is provided by a javascript library that allows you to express dependency. For simple extensions like the previous one, we directly mute the global namespace, but for more complex extensions you could pass a callback to the require([...], &lt;callback&gt;) call, to allow the user to pass configuration information to your plugin.

In Python lang,

require(['a/b', 'c/d'], function( e, f){

could be read as

import a.b as e
import c.d as f

See for example @damianavila "ZenMode" plugin :

// read that as
// import custom.zenmode.main as zenmode

For the quickest

Try to use the following to bind a dropdown list to cell.metadata.difficulty.select.

It should be able to take the four following values :

  • &lt;None&gt;
  • Easy
  • Medium
  • Hard

We will use it to customize the output of the converted notebook depending on the tag on each cell

In [ ]:
%load soln/celldiff.js