.. -*- coding: utf-8 -*-

Javascript

----------

*CubicWeb* uses quite a bit of javascript in its user interface and

ships with jquery (1.3.x) and parts of the jquery UI library, plus a

number of homegrown files and also other third party libraries.

All javascript files are stored in cubicweb/web/data/. There are

around thirty js files there. In a cube it goes to data/.

Obviously one does not want javascript pieces to be loaded all at

once, hence the framework provides a number of mechanisms and

conventions to deal with javascript resources.

Conventions

~~~~~~~~~~~

It is good practice to name cube specific js files after the name of

the cube, like this : 'cube.mycube.js', so as to avoid name clashes.

.. XXX external_resources variable (which needs love)

Server-side Javascript API

~~~~~~~~~~~~~~~~~~~~~~~~~~

Javascript resources are typically loaded on demand, from views. The

request object (available as self._cw from most application objects,

for instance views and entities objects) has a few methods to do that:

* `add_js(self, jsfiles, localfile=True)` which takes a sequence of

  javascript files and writes proper entries into the HTML header

  section. The localfile parameter allows to declare resources which

  are not from web/data (for instance, residing on a content delivery

  network).

* `add_onload(self, jscode)` which adds one raw javascript code

  snippet inline in the html headers. This is quite useful for setting

  up early jQuery(document).ready(...) initialisations.

Javascript events

~~~~~~~~~~~~~~~~~

* ``server-response``: this event is triggered on HTTP responses (both

  standard and ajax). The two following extra parameters are passed

  to callbacks :

  - ``ajax``: a boolean that says if the reponse was issued by an

    ajax request

  - ``node``: the DOM node returned by the server in case of an

    ajax request, otherwise the document itself for standard HTTP

    requests.

Important javascript AJAX APIS

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* `asyncRemoteExec` and `remoteExec` are the base building blocks for

  doing arbitrary async (resp. sync) communications with the server

* `reloadComponent` is a convenience function to replace a DOM node

  with server supplied content coming from a specific registry (this

  is quite handy to refresh the content of some boxes for instances)

* `jQuery.fn.loadxhtml` is an important extension to jQuery which

  allows proper loading and in-place DOM update of xhtml views. It is

  suitably augmented to trigger necessary events, and process CubicWeb

  specific elements such as the facet system, fckeditor, etc.

A simple example with asyncRemoteExec

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the python side, we have to extend the ``BaseController``

class. The ``@jsonize`` decorator ensures that the return value of the

method is encoded as JSON data. By construction, the JSonController

inputs everything in JSON format.

.. sourcecode: python

    from cubicweb.web.views.basecontrollers import JSonController, jsonize

    @monkeypatch(JSonController)

    @jsonize

    def js_say_hello(self, name):

        return u'hello %s' % name

In the javascript side, we do the asynchronous call. Notice how it

creates a `deferred` object. Proper treatment of the return value or

error handling has to be done through the addCallback and addErrback

methods.

.. sourcecode: javascript

    function asyncHello(name) {

        var deferred = asyncRemoteExec('say_hello', name);

        deferred.addCallback(function (response) {

            alert(response);

        });

        deferred.addErrback(function (error) {

            alert('something fishy happened');

        });

     }

     function syncHello(name) {

         alert( remoteExec('say_hello', name) );

     }

Anatomy of a reloadComponent call

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`reloadComponent` allows to dynamically replace some DOM node with new

elements. It has the following signature:

* `compid` (mandatory) is the name of the component to be reloaded

* `rql` (optional) will be used to generate a result set given as

  argument to the selected component

* `registry` (optional) defaults to 'components' but can be any other

  valid registry name

* `nodeid` (optional) defaults to compid + 'Component' but can be any

  explicitly specified DOM node id

* `extraargs` (optional) should be a dictionary of values that will be

  given to the cell_call method of the component

A simple reloadComponent example

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The server side implementation of `reloadComponent` is the

js_component method of the JSonController.

The following function implements a two-steps method to delete a

standard bookmark and refresh the UI, while keeping the UI responsive.

.. sourcecode:: javascript

    function removeBookmark(beid) {

        d = asyncRemoteExec('delete_bookmark', beid);

        d.addCallback(function(boxcontent) {

	    reloadComponent('bookmarks_box', '', 'boxes', 'bookmarks_box');

            document.location.hash = '#header';

            updateMessage(_("bookmark has been removed"));

         });

    }

`reloadComponent` is called with the id of the bookmark box as

argument, no rql expression (because the bookmarks display is actually

independant of any dataset context), a reference to the 'boxes'

registry (which hosts all left, right and contextual boxes) and

finally an explicit 'bookmarks_box' nodeid argument that stipulates

the target DOM node.

Anatomy of a loadxhtml call

~~~~~~~~~~~~~~~~~~~~~~~~~~~

`jQuery.fn.loadxhtml` is an important extension to jQuery which allows

proper loading and in-place DOM update of xhtml views. The existing

`jQuery.load`_ function does not handle xhtml, hence the addition. The

API of loadxhtml is roughly similar to that of `jQuery.load`_.

.. _`jQuery.load`: http://api.jquery.com/load/

* `url` (mandatory) should be a complete url (typically referencing

  the JSonController, but this is not strictly mandatory)

* `data` (optional) is a dictionary of values given to the

  controller specified through an `url` argument; some keys may have a

  special meaning depending on the choosen controller (such as `fname`

  for the JSonController); the `callback` key, if present, must refer

  to a function to be called at the end of loadxhtml (more on this

  below)

* `reqtype` (optional) specifies the request method to be used (get or

  post); if the argument is 'post', then the post method is used,

  otherwise the get method is used

* `mode` (optional) is one of `replace` (the default) which means the

  loaded node will replace the current node content, `swap` to replace

  the current node with the loaded node, and `append` which will

  append the loaded node to the current node content

About the `callback` option:

* it is called with two parameters: the current node, and a list

  containing the loaded (and post-processed node)

* whenever is returns another function, this function is called in

  turn with the same parameters as above

This mechanism allows callback chaining.

A simple example with loadxhtml

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here we are concerned with the retrieval of a specific view to be

injected in the live DOM. The view will be of course selected

server-side using an entity eid provided by the client side.

.. sourcecode:: python

    from cubicweb import typed_eid

    from cubicweb.web.views.basecontrollers import JSonController, xhtmlize

    @monkeypatch(JSonController)

    @xhtmlize

    def js_frob_status(self, eid, frobname):

        entity = self._cw.entity_from_eid(typed_eid(eid))

        return entity.view('frob', name=frobname)

.. sourcecode:: javascript

    function update_some_div(divid, eid, frobname) {

        var params = {fname:'frob_status', eid: eid, frobname:frobname};

        jQuery('#'+divid).loadxhtml(JSON_BASE_URL, params, 'post');

     }

In this example, the url argument is the base json url of a cube

instance (it should contain something like

`http://myinstance/json?`). The actual JSonController method name is

encoded in the `params` dictionary using the `fname` key.

A more real-life example

~~~~~~~~~~~~~~~~~~~~~~~~

A frequent need of Web 2 applications is the delayed (or demand

driven) loading of pieces of the DOM. This is typically achieved using

some preparation of the initial DOM nodes, jQuery event handling and

proper use of loadxhtml.

We present here a skeletal version of the mecanism used in CubicWeb

and available in web/views/tabs.py, in the `LazyViewMixin` class.

.. sourcecode:: python

    def lazyview(self, vid, rql=None):

        """ a lazy version of wview """

        w = self.w

        self._cw.add_js('cubicweb.lazy.js')

        urlparams = {'vid' : vid, 'fname' : 'view'}

        if rql is not None:

            urlparams['rql'] = rql

        w(u'<div id="lazy-%s" cubicweb:loadurl="%s">' % (

            vid, xml_escape(self._cw.build_url('json', **urlparams))))

        w(u'</div>')

        self._cw.add_onload(u"""

            jQuery('#lazy-%(vid)s').bind('%(event)s', function() {

                   load_now('#lazy-%(vid)s');});"""

            % {'event': 'load_%s' % vid, 'vid': vid})

This creates a `div` with a specific event associated to it.

The full version deals with:

* optional parameters such as an entity eid, an rset

* the ability to further reload the fragment

* the ability to display a spinning wheel while the fragment is still

  not loaded

* handling of browsers that do not support ajax (search engines,

  text-based browsers such as lynx, etc.)

The javascript side is quite simple, due to loadxhtml awesomeness.

.. sourcecode:: javascript

    function load_now(eltsel) {

        var lazydiv = jQuery(eltsel);

        lazydiv.loadxhtml(lazydiv.attr('cubicweb:loadurl'));

    }

This is all significantly different of the previous `simple example`

(albeit this example actually comes from real-life code).

Notice how the `cubicweb:loadurl` is used to convey the url

information. The base of this url is similar to the global javascript

JSON_BASE_URL. According to the pattern described earlier,

the `fname` parameter refers to the standard `js_view` method of the

JSonController. This method renders an arbitrary view provided a view

id (or `vid`) is provided, and most likely an rql expression yielding

a result set against which a proper view instance will be selected.

The `cubicweb:loadurl` is one of the 29 attributes extensions to XHTML

in a specific cubicweb namespace. It is a means to pass information

without breaking HTML nor XHTML compliance and without resorting to

ungodly hacks.

Given all this, it is easy to add a small nevertheless useful feature

to force the loading of a lazy view (for instance, a very

computation-intensive web page could be scinded into one fast-loading

part and a delayed part).

On the server side, a simple call to a javascript function is

sufficient.

.. sourcecode:: python

    def forceview(self, vid):

        """trigger an event that will force immediate loading of the view

        on dom readyness

        """

        self._cw.add_onload("trigger_load('%s');" % vid)

The browser-side definition follows.

.. sourcecode:: javascript

    function trigger_load(divid) {

        jQuery('#lazy-' + divd).trigger('load_' + divid);

    }

.. XXX userCallback / user_callback

Javascript library: overview

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* jquery.* : jquery and jquery UI library

* cubicweb.ajax.js : concentrates all ajax related facilities (it

  extends jQuery with the loahxhtml function, provides a handfull of

  high-level ajaxy operations like asyncRemoteExec, reloadComponent,

  replacePageChunk, getDomFromResponse)

* cubicweb.python.js : adds a number of practical extension to stdanrd

  javascript objects (on Date, Array, String, some list and dictionary

  operations), and a pythonesque way to build classes. Defines a

  CubicWeb namespace.

* cubicweb.htmlhelpers.js : a small bag of convenience functions used

  in various other cubicweb javascript resources (baseuri, progress

  cursor handling, popup login box, html2dom function, etc.)

* cubicweb.widgets.js : provides a widget namespace and constructors

  and helpers for various widgets (mainly facets and timeline)

* cubicweb.edition.js : used by edition forms

* cubicweb.preferences.js : used by the preference form

* cubicweb.facets.js : used by the facets mechanism

There is also javascript support for massmailing, gmap (google maps),

fckcwconfig (fck editor), timeline, calendar, goa (CubicWeb over

AppEngine), flot (charts drawing), tabs and bookmarks.

API

~~~

.. toctree::

    :maxdepth: 1

    js_api/index