.. -*- 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 thirparty
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)

CubicWeb 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.

CubicWeb 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 AJAX APIS
~~~~~~~~~~~~~~~~~~~

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

* `asyncRemoteExec` and `remoteExec` are the base building blocks for
  doing arbitrary async (resp. sync) communications with the server

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 async_hello(name) {
        var deferred = asyncRemoteExec('say_hello', name);
        deferred.addCallback(function (response) {
            alert(response);
        });
        deferred.addErrback(function () {
            alert('something fishy happened');
        });
     }

     function sync_hello(name) {
         alert( remoteExec('say_hello', name) );
     }

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` dictionnary using the `fname` key.

A more real-life example from CubicWeb
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A frequent use case of Web 2 applications is the delayed (or
on-demand) 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 an specific event associated to it.

The full version deals with:

* optional parameters such as an rql expression, 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).

In 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);
    }


Anatomy of a lodxhtml call
~~~~~~~~~~~~~~~~~~~~~~~~~~

The loadxhtml extension to jQuery accept many parameters with rich
semantics. Let us detail these.

* `url` (mandatory) should be a complete url, typically based on the
  JSonController, but this is not strictly mandatory

* `data` (optional) is a dictionnary 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 mecanism allows callback chaining.


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.