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# YUI Library Examples: Overlay: IO Plugin

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## Overlay: IO Plugin

This example shows how you can use Widget's plugin infrastructure to add additional features to an existing widget.

We create an IO plugin class for `Overlay` called `StdModIOPlugin`. The plugin adds IO capabilities to the Overlay, bound to one of its standard module sections (header, body or footer).

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### Creating an IO Plugin For Overlay

#### Setting Up The YUI Instance

For this example, we'll pull in `overlay`; the `io`, `json` and `substitute` utility modules and the `plugin` module. The `io` module provides the XHR support we need for the IO plugin. The `json` and `substitute` modules provide the support we need to parse/transform JSON responses into HTML. The `Plugin` base class is the class we'll extend to create our io plugin class for `Overlay`. The code to set up our sandbox instance is shown below:

YUI({...}).use("overlay", "substitute", "io", "json", "plugin", function(Y) { // We'll write our code here, after pulling in the default Overlay widget, the IO utility, the Plugin base class along with the Substitute and JSON utilities }

Using the `overlay` module will also pull down the default CSS required for overlay, on top of which we only need to add our required look/feel CSS for the example.

#### StdModIOPlugin Class Structure

The `StdModIOPlugin` class will extend the `Plugin` base class. Since `Plugin` derives from `Base`, we follow the same pattern we use for widgets and other utilities which extend Base to setup our new class.

Namely:

- Setting up the constructor to invoke the superclass constructor
- Setting up a `NAME` property, to identify the class
- Setting up the default attributes, using the `ATTRS` property
- Providing prototype implementations for anything we want executed during initialization and destruction using the `initializer` and `destructor` lifecycle methods

Additionally, since this is a plugin, we provide a `NS` property for the class, which defines the property which will refer to the `StdModIOPlugin` instance on the host class (e.g. `overlay.io` will be an instance of `StdModIOPlugin`)

. /* Standard Module IO Plugin Constructor */ function StdModIOPlugin(config) { StdModIOPlugin.superclass.constructor.apply(this, arguments); } /* * The namespace for the plugin. This will be the property on the widget, which will * reference the plugin instance, when it's plugged in */ StdModIOPlugin.NS = "io"; /* * The NAME of the StdModIOPlugin class. Used to prefix events generated * by the plugin class. */ StdModIOPlugin.NAME = "stdModIOPlugin"; /* * The default set of attributes for the StdModIOPlugin class. */ StdModIOPlugin.ATTRS = { uri : {...}, cfg : {...}, formatter : {...}, section: {...}, loading: {...} }; /* Extend the base plugin class */ Y.extend(StdModIOPlugin, Y.Plugin, { // Lifecycle methods. initializer: function() {...}, // IO Plugin specific methods refresh : function() {...}, // Default IO transaction handlers _defSuccessHandler : function(id, o) {...}, _defFailureHandler : function(id, o) {...}, _defStartHandler : function(id, o) {...}, _defCompleteHandler : function(id, o) {...}, _defFormatter : function(val) {...} });

#### Plugin Attributes

The `StdModIOPlugin` is a fairly simple plugin class. It provides incremental functionality. It does not need to modify the behavior of any methods on the host Overlay instance, or monitor any Overlay events (unlike the AnimPlugin example).

It sets up the following attributes, which are used to control how the IO plugin's `refresh` method behaves:

uri
  The uri to use for the io request
cfg
  The io configuration object, to pass to io when initiating a transaction
formatter
  The formatter to use to formatting response data. The default implementation simply passes back the response data passed in, unchanged.
section
  The Standard Module section to which the io plugin instance is bound. Response data will be used to populate this section, after passing through the configured formatter.
loading
  The default content to display while an io transaction is in progress

In terms of code, the attributes for the plugin are set up using the standard `ATTRS` property:

StdModIOPlugin.ATTRS = { /* * The uri to use for the io request */ uri : { value:null }, /* * The io configuration object, to pass to io when initiating a transaction */ cfg : { value:null }, /* * The default formatter to use when formatting response data. The default * implementation simply passes back the response data passed in. */ formatter : { valueFn: function() { return this._defFormatter; } }, /* * The Standard Module section to which the io plugin instance is bound. * Response data will be used to populate this section, after passing through * the configured formatter. */ section: { value:StdMod.BODY, validator: function(val) { return (!val || val == StdMod.BODY || val == StdMod.HEADER || val == StdMod.FOOTER); } }, /* * The default loading indicator to use, when an io transaction is in progress. */ loading: { value: '<img class="yui-loading" width="32px" height="32px" src="assets/img/ajax-loader.gif">' } };

The `formatter` attribute uses `valueFn` to define an instance based default value; pointing to the `_defFormatter` method on the `StdModIOPlugin` instance.

#### Lifecycle Methods: initializer, destructor

For the purposes of this example, the `initializer` for the plugin activates the Flash based XDR transport so that the plugin is able to dispatch both in-domain and cross-domain requests (the transport used for any particular uri is controlled through the plugin's `cfg` attribute).

The `destructor` terminates any existing transaction, if active when the plugin is destroyed (unplugged).

initializer: function() { Y.io.transport({ id:'flash', yid: Y.id, src:'../../build/io/IO.swf?stamp=' + (new Date()).getTime() }); } /* * Destruction code. Terminates the activeIO transaction if it exists */ destructor : function() { if (this._activeIO) { Y.io.abort(this._activeIO); this._activeIO = null; } },

#### The refresh Method

The `refresh` method is the main public method which the plugin provides. It's responsible for dispatching the IO request, using the current state of the attributes defined of the plugin. Users will end up invoking the method from the plugin instance attached to the Overlay (`overlay.io.refresh()`).

refresh : function() { section = this.get("section"); if (section && !this._activeIO) { var uri = this.get("uri"); if (uri) { cfg = this.get("cfg") || {}; cfg.on = cfg.on || {}; cfg.on.start = cfg.on.start || Y.bind(this._defStartHandler, this); cfg.on.complete = cfg.on.complete || Y.bind(this._defCompleteHandler, this); cfg.on.success = cfg.on.success || Y.bind(this._defSuccessHandler, this); cfg.on.failure = cfg.on.failure || Y.bind(this._defFailureHandler, this); cfg.method = cfg.method; // io defaults to "GET" if not defined Y.io(uri, cfg); } } }

The `refresh` method, as implemented for the scope of this example, sets up the io configuration object for the transaction it is about to dispatch, filling in the default handlers for io's `start`, `complete`, `success` and `failure` events, if the user does not provide custom implementations.

#### The Default IO Event Handlers

The default success listener, pulls the response data from the response object, and uses it to update the content in the Overlay section defined by the `section` attribute. The response data is passed through the `formatter` configured for the plugin, converting it to the desired output format:

_defSuccessHandler : function(id, o) { var response = o.responseXML || o.responseText; var section = this.get("section"); var formatter = this.get("formatter"); // Invoke Overlay method to set content in the currently configured section this.get("host").setStdModContent(section, formatter(response)); }

The default failure listener, displays an error message in the currently configured `section`, when io communication fails:

_defFailureHandler : function(id, o) { this.get("host").setStdModContent(this.get("section"), "Failed to retrieve content"); }

The default start event listener renders the `loading` content, which remains in place while the transaction is in process, and also stores a reference to the "inprogress" io transaction:

_defStartHandler : function(id, o) { this._activeIO = o; this.get("host").setStdModContent(this.get("section"), this.get("loading")); },

The default complete event listener clears out the "inprogress" io transaction object:

_defCompleteHandler : function(id, o) { this._activeIO = null; }

#### Using the Plugin

All objects derived from Base are Plugin Hosts. They provide `plug` and `unplug` methods to allow users to add/remove plugins to/from existing instances. They also allow the user to specify the set of plugins to be applied to a new instance, along with their configurations, as part of the constructor arguments.

In this example, we'll create a new instance of an Overlay:

/* Create a new Overlay instance, with content generated from script */ var overlay = new Y.Overlay({ width:"40em", visible:false, align: { node:"#show", points: [Y.WidgetPositionExt.TL, Y.WidgetPositionExt.BL] }, zIndex:10, headerContent: generateHeaderMarkup(), bodyContent: "Feed data will be displayed here" });

And then use the `plug` method to add the `StdModIOPlugin`, providing it with a configuration to use when sending out io transactions (The Animation Plugin example shows how you could do the same thing during construction):

/* * Add the Standard Module IO Plugin, and configure it to use flash, and a formatter specific * to the pipes response we're expecting from the uri request we'll send out. */ overlay.plug({ fn:StdModIOPlugin, cfg:{ uri : pipes.baseUri + pipes.feeds["ynews"].uri, cfg:{ xdr: { use:'flash' } }, formatter: pipes.formatter } });

For this example, the io plugin is configured to use the `flash` cross-domain transport, to send out requests to the pipes API for the feed the user selects from the dropdown.

#### Getting Feed Data Through Pipes

We setup an object (`pipes`) to hold the feed URIs, which can be looked up and passed to the plugin to dispatch requests for new data:

/* The Pipes feed URIs to be used to dispatch io transactions */ var pipes = { baseUri : 'http:/'+'/pipes.yahooapis.com/pipes/pipe.run?_id=6b7b2c6a32f5a12e7259c36967052387&_render=json&url=http:/'+'/', feeds : { ynews : { title: 'Yahoo! US News', uri: 'rss.news.yahoo.com/rss/us' }, yui : { title: 'YUI Blog', uri: 'feeds.yuiblog.com/YahooUserInterfaceBlog' }, slashdot : { title: 'Slashdot', uri: 'rss.slashdot.org/Slashdot/slashdot' }, ... }, ...

The data structure also holds the default formatter (`pipes.formatter`) required to convert the JSON responses from the above URIs to HTML. The JSON utility is first used to parse the json response string. The resulting object is iterated around, using Y.each, and substitute is used to generate the list markup:

... // The default formatter, responsible for converting the JSON responses received, // into HTML. JSON is used for the parsing step, and substitute for some basic // templating functionality formatter : function (val) { var formatted = "Error parsing feed data"; try { var json = Y.JSON.parse(val); if (json && json.count) { var html = ['<ul class="yui-feed-data">']; var linkTemplate = '<li><a href="{link}" target="_blank">{title}</a></li>'; // Loop around all the items returned, and feed them into the template above, // using substitute. Y.each(json.value.items, function(v, i) { if (i < 10) { html.push(Y.substitute(linkTemplate, v)); } }); html.push("</ul>"); formatted = html.join(""); } else { formatted = "No Data Available"; } } catch(e) { formatted = "Error parsing feed data"; } return formatted; }

The `change` handler for the select dropdown binds everything together, taking the currently selected feed, constructing the URI for the feed, setting it on the plugin, and sending out the request:

/* Handle select change */ Y.on("change", function(e) { var val = this.get("value"); if (val != -1) { // Set the new URI value on the io plugin overlay.io.set("uri", pipes.baseUri + pipes.feeds[val].uri); // Send out a request to refresh the current section's contents overlay.io.refresh(); } }, "#feedSelector");

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