# Yahoo! UI Library

### get 2.5.1

Yahoo! UI Library > get > Get.js (source view)

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    /**
     * Provides a mechanism to fetch remote resources and
     * insert them into a document
     * @module get
     * @requires yahoo
     */

    /**
     * Fetches and inserts one or more script or link nodes into the document
     * @namespace YAHOO.util
     * @class YAHOO.util.Get
     */
    YAHOO.util.Get = function() {

        /**
         * hash of queues to manage multiple requests
         * @property queues
         * @private
         */
        var queues={},

        /**
         * queue index used to generate transaction ids
         * @property qidx
         * @type int
         * @private
         */
            qidx=0,

        /**
         * node index used to generate unique node ids
         * @property nidx
         * @type int
         * @private
         */
            nidx=0,

            // ridx=0,

            // sandboxFrame=null,

        /**
         * interal property used to prevent multiple simultaneous purge
         * processes
         * @property purging
         * @type boolean
         * @private
         */
            purging=false,

            ua=YAHOO.env.ua,

            lang=YAHOO.lang;

        /**
         * Generates an HTML element, this is not appended to a document
         * @method _node
         * @param type {string} the type of element
         * @param attr {string} the attributes
         * @param win {Window} optional window to create the element in
         * @return {HTMLElement} the generated node
         * @private
         */
        var _node = function(type, attr, win) {
            var w = win || window, d=w.document, n=d.createElement(type);

            for (var i in attr) {
                if (attr[i] && YAHOO.lang.hasOwnProperty(attr, i)) {
                    n.setAttribute(i, attr[i]);
                }
            }

            return n;
        };

        /**
         * Generates a link node
         * @method _linkNode
         * @param url {string} the url for the css file
         * @param win {Window} optional window to create the node in
         * @return {HTMLElement} the generated node
         * @private
         */
        var _linkNode = function(url, win, charset) {
            var c = charset || "utf-8";
            return _node("link", {
                    "id":      "yui__dyn_" + (nidx++),
                    "type":    "text/css",
                    "charset": c,
                    "rel":     "stylesheet",
                    "href":    url
                }, win);
        };

        /**
         * Generates a script node
         * @method _scriptNode
         * @param url {string} the url for the script file
         * @param win {Window} optional window to create the node in
         * @return {HTMLElement} the generated node
         * @private
         */
        var _scriptNode = function(url, win, charset) {
            var c = charset || "utf-8";
            return _node("script", {
                    "id":      "yui__dyn_" + (nidx++),
                    "type":    "text/javascript",
                    "charset": c,
                    "src":     url
                }, win);
        };

        /**
         * Returns the data payload for callback functions
         * @method _returnData
         * @private
         */
        var _returnData = function(q, msg) {
            return {
                    tId: q.tId,
                    win: q.win,
                    data: q.data,
                    nodes: q.nodes,
                    msg: msg,
                    purge: function() {
                        _purge(this.tId);
                    }
                };
        };

        var _get = function(nId, tId) {
            var q = queues[tId],
                n = (lang.isString(nId)) ? q.win.document.getElementById(nId) : nId;
            if (!n) {
                _fail(tId, "target node not found: " + nId);
            }

            return n;
        };

        /*
         * The request failed, execute fail handler with whatever
         * was accomplished.  There isn't a failure case at the
         * moment unless you count aborted transactions
         * @method _fail
         * @param id {string} the id of the request
         * @private
         */
        var _fail = function(id, msg) {
            YAHOO.log("get failure: " + msg, "warn", "Get");
            var q = queues[id];
            // execute failure callback
            if (q.onFailure) {
                var sc=q.scope || q.win;
                q.onFailure.call(sc, _returnData(q, msg));
            }
        };

        /**
         * The request is complete, so executing the requester's callback
         * @method _finish
         * @param id {string} the id of the request
         * @private
         */
        var _finish = function(id) {
            YAHOO.log("Finishing transaction " + id);
            var q = queues[id];
            q.finished = true;

            if (q.aborted) {
                var msg = "transaction " + id + " was aborted";
                _fail(id, msg);
                return;
            }

            // execute success callback
            if (q.onSuccess) {
                var sc=q.scope || q.win;
                q.onSuccess.call(sc, _returnData(q));
            }
        };

        /**
         * Loads the next item for a given request
         * @method _next
         * @param id {string} the id of the request
         * @param loaded {string} the url that was just loaded, if any
         * @private
         */
        var _next = function(id, loaded) {
            YAHOO.log("_next: " + id + ", loaded: " + loaded, "info", "Get");
            var q = queues[id];

            if (q.aborted) {
                var msg = "transaction " + id + " was aborted";
                _fail(id, msg);
                return;
            }

            if (loaded) {
                q.url.shift();
                if (q.varName) {
                    q.varName.shift();
                }
            } else {
                // This is the first pass: make sure the url is an array
                q.url = (lang.isString(q.url)) ? [q.url] : q.url;
                if (q.varName) {
                    q.varName = (lang.isString(q.varName)) ? [q.varName] : q.varName;
                }
            }

            var w=q.win, d=w.document, h=d.getElementsByTagName("head")[0], n;

            if (q.url.length === 0) {
                // Safari 2.x workaround - There is no way to know when
                // a script is ready in versions of Safari prior to 3.x.
                // Adding an extra node reduces the problem, but doesn't
                // eliminate it completely because the browser executes
                // them asynchronously.
                if (q.type === "script" && ua.webkit && ua.webkit < 420 &&
                        !q.finalpass && !q.varName) {
                    // Add another script node.  This does not guarantee that the
                    // scripts will execute in order, but it does appear to fix the
                    // problem on fast connections more effectively than using an
                    // arbitrary timeout.  It is possible that the browser does
                    // block subsequent script execution in this case for a limited
                    // time.
                    var extra = _scriptNode(null, q.win, q.charset);
                    extra.innerHTML='YAHOO.util.Get._finalize("' + id + '");';
                    q.nodes.push(extra); h.appendChild(extra);

                } else {
                    _finish(id);
                }

                return;
            }

            var url = q.url[0];
            YAHOO.log("attempting to load " + url, "info", "Get");

            if (q.type === "script") {
                n = _scriptNode(url, w, q.charset);
            } else {
                n = _linkNode(url, w, q.charset);
            }

            // track this node's load progress
            _track(q.type, n, id, url, w, q.url.length);

            // add the node to the queue so we can return it to the user supplied callback
            q.nodes.push(n);

            // add it to the head or insert it before 'insertBefore'
            if (q.insertBefore) {
                var s = _get(q.insertBefore, id);
                if (s) {
                    s.parentNode.insertBefore(n, s);
                }
            } else {
                h.appendChild(n);
            }

            YAHOO.log("Appending node: " + url, "info", "Get");

            // FireFox does not support the onload event for link nodes, so there is
            // no way to make the css requests synchronous. This means that the css
            // rules in multiple files could be applied out of order in this browser
            // if a later request returns before an earlier one.  Safari too.
            if ((ua.webkit || ua.gecko) && q.type === "css") {
                _next(id, url);
            }
        };

        /**
         * Removes processed queues and corresponding nodes
         * @method _autoPurge
         * @private
         */
        var _autoPurge = function() {

            if (purging) {
                return;
            }

            purging = true;
            for (var i in queues) {
                var q = queues[i];
                if (q.autopurge && q.finished) {
                    _purge(q.tId);
                    delete queues[i];
                }
            }

            purging = false;
        };

        /**
         * Removes the nodes for the specified queue
         * @method _purge
         * @private
         */
        var _purge = function(tId) {
            var q=queues[tId];
            if (q) {
                var n=q.nodes, l=n.length, d=q.win.document,
                    h=d.getElementsByTagName("head")[0];

                if (q.insertBefore) {
                    var s = _get(q.insertBefore, tId);
                    if (s) {
                        h = s.parentNode;
                    }
                }

                for (var i=0; i<l; i=i+1) {
                    h.removeChild(n[i]);
                }
            }
            q.nodes = [];
        };

        /**
         * Saves the state for the request and begins loading
         * the requested urls
         * @method queue
         * @param type {string} the type of node to insert
         * @param url {string} the url to load
         * @param opts the hash of options for this request
         * @private
         */
        var _queue = function(type, url, opts) {

            var id = "q" + (qidx++);
            opts = opts || {};

            if (qidx % YAHOO.util.Get.PURGE_THRESH === 0) {
                _autoPurge();
            }

            queues[id] = lang.merge(opts, {
                tId: id,
                type: type,
                url: url,
                finished: false,
                nodes: []
            });

            var q = queues[id];
            q.win = q.win || window;
            q.scope = q.scope || q.win;
            q.autopurge = ("autopurge" in q) ? q.autopurge :
                          (type === "script") ? true : false;

            lang.later(0, q, _next, id);

            return {
                tId: id
            };
        };

        /**
         * Detects when a node has been loaded.  In the case of
         * script nodes, this does not guarantee that contained
         * script is ready to use.
         * @method _track
         * @param type {string} the type of node to track
         * @param n {HTMLElement} the node to track
         * @param id {string} the id of the request
         * @param url {string} the url that is being loaded
         * @param win {Window} the targeted window
         * @param qlength the number of remaining items in the queue,
         * including this one
         * @param trackfn {Function} function to execute when finished
         * the default is _next
         * @private
         */
        var _track = function(type, n, id, url, win, qlength, trackfn) {
            var f = trackfn || _next;

            // IE supports the readystatechange event for script and css nodes
            if (ua.ie) {
                n.onreadystatechange = function() {
                    var rs = this.readyState;
                    if ("loaded" === rs || "complete" === rs) {
                        YAHOO.log(id + " onload " + url, "info", "Get");
                        f(id, url);
                    }
                };

            // webkit prior to 3.x is problemmatic
            } else if (ua.webkit) {

                if (type === "script") {

                    // Safari 3.x supports the load event for script nodes (DOM2)
                    if (ua.webkit >= 420) {

                        n.addEventListener("load", function() {
                            YAHOO.log(id + " DOM2 onload " + url, "info", "Get");
                            f(id, url);
                        });

                    // Nothing can be done with Safari < 3.x except to pause and hope
                    // for the best, particularly after last script is inserted. The
                    // scripts will always execute in the order they arrive, not
                    // necessarily the order in which they were inserted.  To support
                    // script nodes with complete reliability in these browsers, script
                    // nodes either need to invoke a function in the window once they
                    // are loaded or the implementer needs to provide a well-known
                    // property that the utility can poll for.
                    } else {
                        // Poll for the existence of the named variable, if it
                        // was supplied.
                        var q = queues[id];
                        if (q.varName) {
                            var freq=YAHOO.util.Get.POLL_FREQ;
                            YAHOO.log("Polling for " + q.varName[0]);
                            q.maxattempts = YAHOO.util.Get.TIMEOUT/freq;
                            q.attempts = 0;
                            q._cache = q.varName[0].split(".");
                            q.timer = lang.later(freq, q, function(o) {
                                var a=this._cache, l=a.length, w=this.win, i;
                                for (i=0; i<l; i=i+1) {
                                    w = w[a[i]];
                                    if (!w) {
                                        // if we have exausted our attempts, give up
                                        this.attempts++;
                                        if (this.attempts++ > this.maxattempts) {
                                            var msg = "Over retry limit, giving up";
                                            q.timer.cancel();
                                            _fail(id, msg);
                                        } else {
                                            YAHOO.log(a[i] + " failed, retrying");
                                        }
                                        return;
                                    }
                                }

                                YAHOO.log("Safari poll complete");

                                q.timer.cancel();
                                f(id, url);

                            }, null, true);
                        } else {
                            lang.later(YAHOO.util.Get.POLL_FREQ, null, f, [id, url]);
                        }
                    }
                }

            // FireFox and Opera support onload (but not DOM2 in FF) handlers for
            // script nodes.  Opera, but not FF, supports the onload event for link
            // nodes.
            } else {
                n.onload = function() {
                    YAHOO.log(id + " onload " + url, "info", "Get");
                    f(id, url);
                };
            }
        };

        return {

            /**
             * The default poll freqency in ms, when needed
             * @property POLL_FREQ
             * @static
             * @type int
             * @default 10
             */
            POLL_FREQ: 10,

            /**
             * The number of request required before an automatic purge.
             * property PURGE_THRESH
             * @static
             * @type int
             * @default 20
             */
            PURGE_THRESH: 20,

            /**
             * The length time to poll for varName when loading a script in
             * Safari 2.x before the transaction fails.
             * property TIMEOUT
             * @static
             * @type int
             * @default 2000
             */
            TIMEOUT: 2000,

            /**
             * Called by the the helper for detecting script load in Safari
             * @method _finalize
             * @param id {string} the transaction id
             * @private
             */
            _finalize: function(id) {
                YAHOO.log(id + " finalized ", "info", "Get");
                lang.later(0, null, _finish, id);
            },

            /**
             * Abort a transaction
             * @method abort
             * @param {string|object} either the tId or the object returned from
             * script() or css()
             */
            abort: function(o) {
                var id = (lang.isString(o)) ? o : o.tId;
                var q = queues[id];
                if (q) {
                    YAHOO.log("Aborting " + id, "info", "Get");
                    q.aborted = true;
                }
            },

            /**
             * Fetches and inserts one or more script nodes into the head
             * of the current document or the document in a specified window.
             *
             * @method script
             * @static
             * @param url {string|string[]} the url or urls to the script(s)
             * @param opts {object} Options:
             * <dl>
             * <dt>onSuccess</dt>
             * <dd>
             * callback to execute when the script(s) are finished loading
             * The callback receives an object back with the following
             * data:
             * <dl>
             * <dt>win</dt>
             * <dd>the window the script(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove the nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>onFailure</dt>
             * <dd>
             * callback to execute when the script load operation fails
             * The callback receives an object back with the following
             * data:
             * <dl>
             * <dt>win</dt>
             * <dd>the window the script(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted successfully</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove any nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>scope</dt>
             * <dd>the execution context for the callbacks</dd>
             * <dt>win</dt>
             * <dd>a window other than the one the utility occupies</dd>
             * <dt>autopurge</dt>
             * <dd>
             * setting to true will let the utilities cleanup routine purge
             * the script once loaded
             * </dd>
             * <dt>data</dt>
             * <dd>
             * data that is supplied to the callback when the script(s) are
             * loaded.
             * </dd>
             * <dt>varName</dt>
             * <dd>
             * variable that should be available when a script is finished
             * loading.  Used to help Safari 2.x and below with script load
             * detection.  The type of this property should match what was
             * passed into the url parameter: if loading a single url, a
             * string can be supplied.  If loading multiple scripts, you
             * must supply an array that contains the variable name for
             * each script.
             * </dd>
             * <dt>insertBefore</dt>
             * <dd>node or node id that will become the new node's nextSibling</dd>
             * </dl>
             * <dt>charset</dt>
             * <dd>Node charset, default utf-8</dd>
             * <pre>
             * // assumes yahoo, dom, and event are already on the page
             * &nbsp;&nbsp;YAHOO.util.Get.script(
             * &nbsp;&nbsp;["http://yui.yahooapis.com/2.3.1/build/dragdrop/dragdrop-min.js",
             * &nbsp;&nbsp;&nbsp;"http://yui.yahooapis.com/2.3.1/build/animation/animation-min.js"], &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;onSuccess: function(o) &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;YAHOO.log(o.data); // foo
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new YAHOO.util.DDProxy("dd1"); // also new o.reference("dd1"); would work
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.log("won't cause error because YAHOO is the scope");
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.log(o.nodes.length === 2) // true
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// o.purge(); // optionally remove the script nodes immediately
             * &nbsp;&nbsp;&nbsp;&nbsp;&#125;,
             * &nbsp;&nbsp;&nbsp;&nbsp;onFailure: function(o) &#123;
             * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;YAHOO.log("transaction failed");
             * &nbsp;&nbsp;&nbsp;&nbsp;&#125;,
             * &nbsp;&nbsp;&nbsp;&nbsp;data: "foo",
             * &nbsp;&nbsp;&nbsp;&nbsp;scope: YAHOO,
             * &nbsp;&nbsp;&nbsp;&nbsp;// win: otherframe // target another window/frame
             * &nbsp;&nbsp;&nbsp;&nbsp;autopurge: true // allow the utility to choose when to remove the nodes
             * &nbsp;&nbsp;&#125;);
             * </pre>
             * @return {tId: string} an object containing info about the transaction
             */
            script: function(url, opts) { return _queue("script", url, opts); },

            /**
             * Fetches and inserts one or more css link nodes into the
             * head of the current document or the document in a specified
             * window.
             * @method css
             * @static
             * @param url {string} the url or urls to the css file(s)
             * @param opts Options:
             * <dl>
             * <dt>onSuccess</dt>
             * <dd>
             * callback to execute when the css file(s) are finished loading
             * The callback receives an object back with the following
             * data:
             * <dl>win</dl>
             * <dd>the window the link nodes(s) were inserted into</dd>
             * <dt>data</dt>
             * <dd>the data object passed in when the request was made</dd>
             * <dt>nodes</dt>
             * <dd>An array containing references to the nodes that were
             * inserted</dd>
             * <dt>purge</dt>
             * <dd>A function that, when executed, will remove the nodes
             * that were inserted</dd>
             * <dt>
             * </dl>
             * </dd>
             * <dt>scope</dt>
             * <dd>the execution context for the callbacks</dd>
             * <dt>win</dt>
             * <dd>a window other than the one the utility occupies</dd>
             * <dt>data</dt>
             * <dd>
             * data that is supplied to the callbacks when the nodes(s) are
             * loaded.
             * </dd>
             * <dt>insertBefore</dt>
             * <dd>node or node id that will become the new node's nextSibling</dd>
             * <dt>charset</dt>
             * <dd>Node charset, default utf-8</dd>
             * </dl>
             * <pre>
             *      YAHOO.util.Get.css("http://yui.yahooapis.com/2.3.1/build/menu/assets/skins/sam/menu.css");
             * </pre>
             * <pre>
             *      YAHOO.util.Get.css(["http://yui.yahooapis.com/2.3.1/build/menu/assets/skins/sam/menu.css",
             *                          "http://yui.yahooapis.com/2.3.1/build/logger/assets/skins/sam/logger.css"]);
             * </pre>
             * @return {tId: string} an object containing info about the transaction
             */
            css: function(url, opts) {
                return _queue("css", url, opts);
            }
        };
    }();

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