# Yahoo! UI Library

### io 3.0.0

Yahoo! UI Library > io > io-base.js (source view)
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       /**
       	* Base IO functionality. Provides basic XHR transport support.
       	* @module io
       	* @submodule io-base
       	*/

       /**
    	* The io class is a utility that brokers HTTP requests through a simplified
    	* interface.  Specifically, it allows JavaScript to make HTTP requests to
    	* a resource without a page reload.  The underlying transport for making
    	* same-domain requests is the XMLHttpRequest object.  YUI.io can also use
    	* Flash, if specified as a transport, for cross-domain requests.
    	*
       	* @class io
       	*/

       /**
       	* @event io:start
       	* @description This event is fired by YUI.io when a transaction is initiated.
       	* @type Event Custom
       	*/
       	var E_START = 'io:start',

       /**
       	* @event io:complete
       	* @description This event is fired by YUI.io when a transaction is complete.
       	* Response status and data are accessible, if available.
       	* @type Event Custom
       	*/
       	E_COMPLETE = 'io:complete',

       /**
       	* @event io:success
       	* @description This event is fired by YUI.io when a transaction is complete, and
       	* the HTTP status resolves to HTTP2xx.
       	* @type Event Custom
       	*/
       	E_SUCCESS = 'io:success',

       /**
       	* @event io:failure
       	* @description This event is fired by YUI.io when a transaction is complete, and
       	* the HTTP status resolves to HTTP4xx, 5xx and above.
       	* @type Event Custom
       	*/
       	E_FAILURE = 'io:failure',

       /**
       	* @event io:end
       	* @description This event signifies the end of the transaction lifecycle.  The
       	* transaction transport is destroyed.
       	* @type Event Custom
       	*/
       	E_END = 'io:end',

       	//--------------------------------------
       	//  Properties
       	//--------------------------------------
       /**
       	* @description A transaction counter that increments for each transaction.
       	*
       	* @property transactionId
       	* @private
       	* @static
       	* @type int
       	*/
       	transactionId = 0,

       /**
       	* @description Object of default HTTP headers to be initialized and sent
       	* for all transactions.
       	*
       	* @property _headers
       	* @private
       	* @static
       	* @type object
       	*/
       	_headers = {
       		'X-Requested-With' : 'XMLHttpRequest'
       	},

       /**
       	* @description Object that stores timeout values for any transaction with
       	* a defined "timeout" configuration property.
       	*
       	* @property _timeout
       	* @private
       	* @static
       	* @type object
       	*/
       	_timeout = {},

       	// Window reference
       	w = Y.config.win;

       	//--------------------------------------
       	//  Methods
       	//--------------------------------------
       /**
       	* @description Method for requesting a transaction. _io() is implemented as
       	* yui.io().  Each transaction may include a configuration object.  Its
       	* properties are:
       	*
       	* method: HTTP method verb (e.g., GET or POST). If this property is not
       	*         not defined, the default value will be GET.
       	*
       	* data: This is the name-value string that will be sent as the transaction
        *		data.  If the request is HTTP GET, the data become part of
        *		querystring. If HTTP POST, the data are sent in the message body.
       	*
       	* xdr: Defines the transport to be used for cross-domain requests.  By
       	*      setting this property, the transaction will use the specified
       	*      transport instead of XMLHttpRequest.  Currently, the only alternate
       	*      transport supported is Flash (e.g., { xdr: 'flash' }).
       	*
       	* form: This is a defined object used to process HTML form as data.  The
       	*       properties are:
       	*       {
       	*	      id: object, //HTML form object or id of HTML form
       	*         useDisabled: boolean, //Allow disabled HTML form field values
       	*                      to be sent as part of the data.
    	*       }
    	*
    	* on: This is a defined object used to create and handle specific
    	*     events during a transaction lifecycle.  These events will fire in
    	*     addition to the global io events. The events are:
    	*	  start - This event is fired when a request is sent to a resource.
    	*     complete - This event fires when the transaction is complete.
    	*     success - This event fires when the response status resolves to
    	*               HTTP 2xx.
    	*     failure - This event fires when the response status resolves to
    	*               HTTP 4xx, 5xx; and, for all transaction exceptions,
    	*               including aborted transactions and transaction timeouts.
    	*	  end -  This even is fired at the conclusion of the transaction
       	*			 lifecycle, after a success or failure resolution.
    	*
    	*     The properties are:
    	*     {
       	*       start: function(id, args){},
       	*       complete: function(id, responseobject, args){},
       	*       success: function(id, responseobject, args){},
       	*       failure: function(id, responseobject, args){},
       	*       end: function(id, args){}
       	*     }
       	*	  Each property can reference a function or be written as an
       	*     inline function.
       	*
       	*     context: Object reference for an event handler when it is implemented
       	*              as a method of a base object. Defining "context" will preserve
       	*              the proper reference of "this" used in the event handler.
       	*     headers: This is a defined object of client headers, as many as.
       	*              desired for the transaction.  These headers are sentThe object
       	*              pattern is:
       	*              {
       	*		         header: value
       	*              }
       	*
       	* timeout: This value, defined as milliseconds, is a time threshold for the
       	*          transaction. When this threshold is reached, and the transaction's
       	*          Complete event has not yet fired, the transaction will be aborted.
       	* arguments: Object, array, string, or number passed to all registered
       	*            event handlers.  This value is available as the second
       	*            argument in the "start" and "abort" event handlers; and, it is
       	*            the third argument in the "complete", "success", and "failure"
       	*            event handlers.
       	*
       	* @method _io
       	* @private
       	* @static
    	* @param {string} uri - qualified path to transaction resource.
    	* @param {object} c - configuration object for the transaction.
    	* @param {number} i - transaction id, if already set by queue.
    	* @return object
       	*/
       	function _io(uri, c, i) {
       		var f, o, m;
       			c = c || {};
       			o = _create(c.xdr || c.form, i);
       			m = c.method ? c.method.toUpperCase() : 'GET';

       		if (c.form) {
       			if (c.form.upload) {
       				return Y.io._upload(o, uri, c);
       			}
       			else {
    				f = Y.io._serialize(c.form, c.data);
    				if (m === 'POST') {
    					c.data = f;
    					_setHeader('Content-Type', 'application/x-www-form-urlencoded');
    				}
    				else if (m === 'GET') {
    					uri = _concat(uri, f);
    				}
    			}
    		}
    		else if (c.data && m === 'GET') {
    			uri = _concat(uri, c.data);
    		}

       		if (c.xdr) {
    			if (c.xdr.use === 'native' && window.XDomainRequest || c.xdr.use === 'flash') {
       				return Y.io.xdr(uri, o, c);
    			}
    			if (c.xdr.credentials) {
    				o.c.withCredentials = true;
    			}
       		}

       		o.c.onreadystatechange = function() { _readyState(o, c); };
       		try {
    			o.c.open(m, uri, true);
       		}
       		catch(e0){
    			if (c.xdr) {
    				// This exception is usually thrown by browsers
    				// that do not support native XDR transactions.
    				return _resend(o, uri, c);
    			}
    		}

       		if (c.data && m === 'POST') {
       			_setHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
       		}

       		_setHeaders(o.c, c.headers || {});
    		try {
    			// Using "null" will result in a POST request with
    			// no Content-Length defined.
    	   		o.c.send(c.data || '');
    		}
       		catch(e1) {
    			if (c.xdr) {
    				// This exception is usually thrown by browsers
    				// that do not support native XDR transactions.
    				return _resend(o, uri, c);
    			}
    		}

       		_ioStart(o.id, c);
       		// If config.timeout is defined, and the request is standard XHR,
       		// initialize timeout polling.
       		if (c.timeout) {
       			_startTimeout(o, c.timeout);
       		}

    		return {
    			id: o.id,
    			abort: function() {
    				return o.c ? _ioCancel(o, 'abort') : false;
    			},
    			isInProgress: function() {
    				return o.c ? o.c.readyState !== 4 && o.c.readyState !== 0 : false;
    	   		}
    		}
       	}

       /**
       	* @description Method for creating and subscribing transaction events.
       	*
       	* @method _subscribe
       	* @private
       	* @static
       	* @param {string} e - event to be published
       	* @param {object} c - configuration data subset for event subscription.
       	*
    	* @return void
       	*/
       	function _subscribe(e, c){
       		var evt = new Y.EventTarget().publish('transaction:' + e);
    		evt.subscribe(c.on[e], (c.context || Y), c.arguments);

       		return evt;
       	}

       /**
       	* @description Fires event "io:start" and creates, fires a
       	* transaction-specific start event, if config.on.start is
       	* defined.
       	*
       	* @method _ioStart
       	* @private
       	* @static
       	* @param {number} id - transaction id
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
       	function _ioStart(id, c) {
       		var evt;
       			// Set default value of argument c, property "on" to Object if
       			// the property is null or undefined.
       			c.on = c.on || {};

       		Y.fire(E_START, id);
       		if (c.on.start) {
       			evt = _subscribe('start', c);
       			evt.fire(id);
       		}
       	}

       /**
       	* @description Fires event "io:complete" and creates, fires a
       	* transaction-specific "complete" event, if config.on.complete is
       	* defined.
       	*
       	* @method _ioComplete
       	* @private
       	* @static
       	* @param {object} o - transaction object.
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
       	function _ioComplete(o, c) {
       		var evt,
    			r = o.status ? { status: 0, statusText: o.status } : o.c;
       			// Set default value of argument c, property "on" to Object if
       			// the property is null or undefined.
       			c.on = c.on || {};

       		Y.fire(E_COMPLETE, o.id, r);
       		if (c.on.complete) {
       			evt = _subscribe('complete', c);
       			evt.fire(o.id, r);
       		}
       	}

       /**
       	* @description Fires event "io:success" and creates, fires a
       	* transaction-specific "success" event, if config.on.success is
       	* defined.
       	*
       	* @method _ioSuccess
       	* @private
       	* @static
       	* @param {object} o - transaction object.
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
       	function _ioSuccess(o, c) {
       		var evt;
       			// Set default value of argument c, property "on" to Object if
       			// the property is null or undefined.
       			c.on = c.on || {};

       		Y.fire(E_SUCCESS, o.id, o.c);
       		if (c.on.success) {
       			evt = _subscribe('success', c);
       			evt.fire(o.id, o.c);
       		}

       		_ioEnd(o, c);
       	}

       /**
       	* @description Fires event "io:failure" and creates, fires a
       	* transaction-specific "failure" event, if config.on.failure is
       	* defined.
       	*
       	* @method _ioFailure
       	* @private
       	* @static
       	* @param {object} o - transaction object.
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
       	function _ioFailure(o, c) {
       		var evt,
     			r = o.status ? { status: 0, statusText: o.status } : o.c;
       			// Set default value of argument c, property "on" to Object if
       			// the property is null or undefined.
       			c.on = c.on || {};

       		Y.fire(E_FAILURE, o.id, r);
       		if (c.on.failure) {
       			evt = _subscribe('failure', c);
       			evt.fire(o.id, r);
       		}

       		_ioEnd(o, c);
       	}

       /**
       	* @description Fires event "io:end" and creates, fires a
       	* transaction-specific "end" event, if config.on.end is
       	* defined.
       	*
       	* @method _ioEnd
       	* @private
       	* @static
       	* @param {object} o - transaction object.
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
       	function _ioEnd(o, c) {
       		var evt;
       			// Set default value of argument c, property "on" to Object if
       			// the property is null or undefined.
       			c.on = c.on || {};

       		Y.fire(E_END, o.id);
       		if (c.on.end) {
       			evt = _subscribe('end', c);
       			evt.fire(o.id);
       		}

       		_destroy(o, c.xdr ? true : false );
       	}

       /**
       	* @description Terminates a transaction due to an explicit abort or
       	* timeout.
       	*
       	* @method _ioCancel
       	* @private
       	* @static
    	* @param {object} o - Transaction object generated by _create().
    	* @param {string} s - Identifies timed out or aborted transaction.
       	*
        * @return void
       	*/
       	function _ioCancel(o, s) {
       		if (o && o.c) {
       			o.status = s;
       			o.c.abort();
       		}
       	}

       /**
       	* @description Resends an XDR transaction, using the Flash tranport,
       	* if the native transport fails.
       	*
       	* @method _resend
       	* @private
       	* @static

    	* @param {object} o - Transaction object generated by _create().
    	* @param {string} uri - qualified path to transaction resource.
       	* @param {object} c - configuration object for the transaction.
       	*
        * @return void
       	*/
    	function _resend(o, uri, c) {
    		var id = parseInt(o.id);

    		_destroy(o);
    		c.xdr.use = 'flash';

    		return Y.io(uri, c, id);
    	}

       /**
       	* @description Method that increments _transactionId for each transaction.
       	*
       	* @method _id
       	* @private
       	* @static
        * @return int
       	*/
       	function _id() {
       		var id = transactionId;

       		transactionId++;

       		return id;
       	}

       /**
       	* @description Method that creates a unique transaction object for each
       	* request.
       	*
       	* @method _create
       	* @private
       	* @static
    	* @param {number} c - configuration object subset to determine if
    	*                     the transaction is an XDR or file upload,
    	*                     requiring an alternate transport.
    	* @param {number} i - transaction id
    	* @return object
       	*/
       	function _create(c, i) {
       		var o = {};
    	   		o.id = Y.Lang.isNumber(i) ? i : _id();
    	   		c = c || {};

    		if (!c.use && !c.upload) {
       			o.c = _xhr();
    		}
       		else if (c.use) {
    			if (c.use === 'flash') {
       				o.c = Y.io._transport[c.use];
    			}
    			else if (c.use === 'native' && window.XDomainRequest) {
    				o.c = new XDomainRequest();
    			}
    			else {
    				o.c = _xhr();
    			}
       		}
       		else {
       			o.c = {};
       		}

       		return o;
       	};

       /**
       	* @description Method that creates the XMLHttpRequest transport
       	*
       	* @method _xhr
       	* @private
       	* @static
    	* @return object
       	*/
       	function _xhr() {
       		return w.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
       	}

       /**
       	* @description Method that concatenates string data for HTTP GET transactions.
       	*
       	* @method _concat
       	* @private
       	* @static
    	* @param {string} s - URI or root data.
    	* @param {string} d - data to be concatenated onto URI.
    	* @return int
       	*/
       	function _concat(s, d) {
       		s += ((s.indexOf('?') == -1) ? '?' : '&') + d;
       		return s;
       	}

       /**
       	* @description Method that stores default client headers for all transactions.
       	* If a label is passed with no value argument, the header will be deleted.
       	*
       	* @method _setHeader
       	* @private
       	* @static
    	* @param {string} l - HTTP header
    	* @param {string} v - HTTP header value
    	* @return int
       	*/
       	function _setHeader(l, v) {
       		if (v) {
       			_headers[l] = v;
       		}
       		else {
       			delete _headers[l];
       		}
       	}

       /**
       	* @description Method that sets all HTTP headers to be sent in a transaction.
       	*
       	* @method _setHeaders
       	* @private
       	* @static
    	* @param {object} o - XHR instance for the specific transaction.
    	* @param {object} h - HTTP headers for the specific transaction, as defined
    	*                     in the configuration object passed to YUI.io().
    	* @return void
       	*/
       	function _setHeaders(o, h) {
       		var p;

       		for (p in _headers) {
       			if (_headers.hasOwnProperty(p)) {
       				if (h[p]) {
       					// Configuration headers will supersede IO preset headers,
       					// if headers match.
       					break;
       				}
       				else {
       					h[p] = _headers[p];
       				}
       			}
       		}

       		for (p in h) {
       			if (h.hasOwnProperty(p)) {
       				o.setRequestHeader(p, h[p]);
       			}
       		}
       	}

       /**
       	* @description Starts timeout count if the configuration object
       	* has a defined timeout property.
       	*
       	* @method _startTimeout
       	* @private
       	* @static
    	* @param {object} o - Transaction object generated by _create().
    	* @param {object} c - Configuration object passed to YUI.io().
    	* @return void
       	*/
       	function _startTimeout(o, timeout) {
       		_timeout[o.id] = w.setTimeout(function() { _ioCancel(o, 'timeout'); }, timeout);
       	}

       /**
       	* @description Clears the timeout interval started by _startTimeout().
       	*
       	* @method _clearTimeout
       	* @private
       	* @static
    	* @param {number} id - Transaction id.
    	* @return void
       	*/
       	function _clearTimeout(id) {
       		w.clearTimeout(_timeout[id]);
       		delete _timeout[id];
       	}

       /**
       	* @description Event handler bound to onreadystatechange.
       	*
       	* @method _readyState
       	* @private
       	* @static
    	* @param {object} o - Transaction object generated by _create().
    	* @param {object} c - Configuration object passed to YUI.io().
    	* @return void
       	*/
       	function _readyState(o, c) {
       		if (o.c.readyState === 4) {
       			if (c.timeout) {
       				_clearTimeout(o.id);
       			}

       			w.setTimeout(
       				function() {
       					_ioComplete(o, c);
       					_handleResponse(o, c);
       				}, 0);
       		}
       	}

       /**
       	* @description Method that determines if a transaction response qualifies
       	* as success or failure, based on the response HTTP status code, and
       	* fires the appropriate success or failure events.
       	*
       	* @method _handleResponse
       	* @private
       	* @static
    	* @param {object} o - Transaction object generated by _create().
    	* @param {object} c - Configuration object passed to io().
    	* @return void
       	*/
       	function _handleResponse(o, c) {
       		var status;
       		try{
       			if (o.c.status && o.c.status !== 0) {
       				status = o.c.status;
       			}
       			else {
       				status = 0;
       			}
       		}
       		catch(e) {
       			status = 0;
       		}

       		// IE reports HTTP 204 as HTTP 1223.
       		if (status >= 200 && status < 300 || status === 1223) {
       			_ioSuccess(o, c);
       		}
       		else {
       			_ioFailure(o, c);
       		}
       	}

       	function _destroy(o, transport) {
       		// IE, when using XMLHttpRequest as an ActiveX Object, will throw
       		// a "Type Mismatch" error if the event handler is set to "null".
       		if(w.XMLHttpRequest && !transport) {
       			if (o.c) {
       				o.c.onreadystatechange = null;
       			}
       		}

       		o.c = null;
       		o = null;
       	}

       	_io.start = _ioStart;
    	_io.complete = _ioComplete;
       	_io.success = _ioSuccess;
       	_io.failure = _ioFailure;
       	_io.end = _ioEnd;
       	_io._id = _id;
       	_io._timeout = _timeout;

    	//--------------------------------------
    	//  Begin public interface definition
    	//--------------------------------------
       /**
       	* @description Method that stores default client headers for all transactions.
       	* If a label is passed with no value argument, the header will be deleted.
       	* This is the interface for _setHeader().
       	*
       	* @method header
       	* @public
       	* @static
    	* @param {string} l - HTTP header
    	* @param {string} v - HTTP header value
    	* @return int
       	*/
       	_io.header = _setHeader;

       /**
       	* @description Method for requesting a transaction. This
       	* is the interface for _io().
       	*
       	* @method io
       	* @public
       	* @static
        * @param {string} uri - qualified path to transaction resource.
        * @param {object} c - configuration object for the transaction.
        * @return object
        */
       	Y.io = _io;
    	Y.io.http = _io;

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