# Yahoo! UI Library

### async-queue 3.0.0

Yahoo! UI Library > async-queue > async-queue.js (source view)
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    /**
     * <p>AsyncQueue allows you create a chain of function callbacks executed
     * via setTimeout (or synchronously) that are guaranteed to run in order.
     * Items in the queue can be promoted or removed.  Start or resume the
     * execution chain with run().  pause() to temporarily delay execution, or
     * stop() to halt and clear the queue.</p>
     *
     * @module async-queue
     */

    /**
     * <p>A specialized queue class that supports scheduling callbacks to execute
     * sequentially, iteratively, even asynchronously.</p>
     *
     * <p>Callbacks can be function refs or objects with the following keys.  Only
     * the <code>fn</code> key is required.</p>
     *
     * <ul>
     * <li><code>fn</code> -- The callback function</li>
     * <li><code>context</code> -- The execution context for the callbackFn.</li>
     * <li><code>args</code> -- Arguments to pass to callbackFn.</li>
     * <li><code>timeout</code> -- Millisecond delay before executing callbackFn.
     *                     (Applies to each iterative execution of callback)</li>
     * <li><code>iterations</code> -- Number of times to repeat the callback.
     * <li><code>until</code> -- Repeat the callback until this function returns
     *                         true.  This setting trumps iterations.</li>
     * <li><code>autoContinue</code> -- Set to false to prevent the AsyncQueue from
     *                        executing the next callback in the Queue after
     *                        the callback completes.</li>
     * <li><code>id</code> -- Name that can be used to get, promote, get the
     *                        indexOf, or delete this callback.</li>
     * </ul>
     *
     * @class AsyncQueue
     * @extends EventTarget
     * @constructor
     * @param callback* {Function|Object} 0..n callbacks to seed the queue
     */
    Y.AsyncQueue = function() {
        this._init();
        this.add.apply(this, arguments);
    };

    var Queue   = Y.AsyncQueue,
        EXECUTE = 'execute',
        SHIFT   = 'shift',
        PROMOTE = 'promote',
        REMOVE  = 'remove',

        isObject   = Y.Lang.isObject,
        isFunction = Y.Lang.isFunction;

    /**
     * <p>Static default values used to populate callback configuration properties.
     * Preconfigured defaults include:</p>
     *
     * <ul>
     *  <li><code>autoContinue</code>: <code>true</code></li>
     *  <li><code>iterations</code>: 1</li>
     *  <li><code>timeout</code>: 10 (10ms between callbacks)</li>
     *  <li><code>until</code>: (function to run until iterations &lt;= 0)</li>
     * </ul>
     *
     * @property AsyncQueue.defaults
     * @type {Object}
     * @static
     */
    Queue.defaults = Y.mix({
        autoContinue : true,
        iterations   : 1,
        timeout      : 10,
        until        : function () {
            this.iterations |= 0;
            return this.iterations <= 0;
        }
    }, Y.config.queueDefaults || {});

    Y.extend(Queue, Y.EventTarget, {
        /**
         * Used to indicate the queue is currently executing a callback.
         *
         * @property _running
         * @type {Boolean|Object} true for synchronous callback execution, the
         *                        return handle from Y.later for async callbacks.
         *                        Otherwise false.
         * @protected
         */
        _running : false,

        /**
         * Initializes the AsyncQueue instance properties and events.
         *
         * @method _init
         * @protected
         */
        _init : function () {
            Y.EventTarget.call(this, { emitFacade: true });

            this._q = [];

            /**
             * Callback defaults for this instance.  Static defaults that are not
             * overridden are also included.
             *
             * @property defaults
             * @type {Object}
             */
            this.defaults = {};

            this._initEvents();
        },

        /**
         * Initializes the instance events.
         *
         * @method _initEvents
         * @protected
         */
        _initEvents : function () {
            /*
            this.publish({
                'execute' : { defaultFn : this._defExecFn },
                'shift'   : { defaultFn : this._defShiftFn },
                'add'     : { defaultFn : this._defAddFn },
                'promote' : { defaultFn : this._defPromoteFn },
                'remove'  : { defaultFn : this._defRemoveFn }
            });
            */
            this.publish('execute' , { defaultFn : this._defExecFn, emitFacade: true });
            this.publish('shift'   , { defaultFn : this._defShiftFn, emitFacade: true });
            this.publish('add'     , { defaultFn : this._defAddFn, emitFacade: true });
            this.publish('promote' , { defaultFn : this._defPromoteFn, emitFacade: true });
            this.publish('remove'  , { defaultFn : this._defRemoveFn, emitFacade: true });
        },

        /**
         * Returns the next callback needing execution.  If a callback is
         * configured to repeat via iterations or until, it will be returned until
         * the completion criteria is met.
         *
         * When the queue is empty, null is returned.
         *
         * @method next
         * @return {Function} the callback to execute
         */
        next : function () {
            var callback;

            while (this._q.length) {
                callback = this._q[0] = this._prepare(this._q[0]);
                if (callback && callback.until()) {
                    this.fire(SHIFT, { callback: callback });
                    callback = null;
                } else {
                    break;
                }
            }

            return callback || null;
        },

        /**
         * Default functionality for the &quot;shift&quot; event.  Shifts the
         * callback stored in the event object's <em>callback</em> property from
         * the queue if it is the first item.
         *
         * @method _defShiftFn
         * @param e {Event} The event object
         * @protected
         */
        _defShiftFn : function (e) {
            if (this.indexOf(e.callback) === 0) {
                this._q.shift();
            }
        },

        /**
         * Creates a wrapper function to execute the callback using the aggregated
         * configuration generated by combining the static AsyncQueue.defaults, the
         * instance defaults, and the specified callback settings.
         *
         * The wrapper function is decorated with the callback configuration as
         * properties for runtime modification.
         *
         * @method _prepare
         * @param callback {Object|Function} the raw callback
         * @return {Function} a decorated function wrapper to execute the callback
         * @protected
         */
        _prepare: function (callback) {
            if (isFunction(callback) && callback._prepared) {
                return callback;
            }

            var config = Y.merge(
                Queue.defaults,
                { context : this, args: [], _prepared: true },
                this.defaults,
                (isFunction(callback) ? { fn: callback } : callback)),

                wrapper = Y.bind(function () {
                    if (!wrapper._running) {
                        wrapper.iterations--;
                    }
                    if (isFunction(wrapper.fn)) {
                        wrapper.fn.apply(wrapper.context || Y,
                                         Y.Array(wrapper.args));
                    }
                }, this);

            return Y.mix(wrapper, config);
        },

        /**
         * Sets the queue in motion.  All queued callbacks will be executed in
         * order unless pause() or stop() is called or if one of the callbacks is
         * configured with autoContinue: false.
         *
         * @method run
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        run : function () {
            var callback,
                cont = true;

            for (callback = this.next();
                cont && callback && !this.isRunning();
                callback = this.next())
            {
                cont = (callback.timeout < 0) ?
                    this._execute(callback) :
                    this._schedule(callback);
            }

            if (!callback) {
                /**
                 * Event fired after the last queued callback is executed.
                 * @event complete
                 */
                this.fire('complete');
            }

            return this;
        },

        /**
         * Handles the execution of callbacks. Returns a boolean indicating
         * whether it is appropriate to continue running.
         *
         * @method _execute
         * @param callback {Object} the callback object to execute
         * @return {Boolean} whether the run loop should continue
         * @protected
         */
        _execute : function (callback) {
            this._running = callback._running = true;

            callback.iterations--;
            this.fire(EXECUTE, { callback: callback });

            var cont = this._running && callback.autoContinue;

            this._running = callback._running = false;

            return cont;
        },

        /**
         * Schedules the execution of asynchronous callbacks.
         *
         * @method _schedule
         * @param callback {Object} the callback object to execute
         * @return {Boolean} whether the run loop should continue
         * @protected
         */
        _schedule : function (callback) {
            this._running = Y.later(callback.timeout, this, function () {
                if (this._execute(callback)) {
                    this.run();
                }
            });

            return false;
        },

        /**
         * Determines if the queue is waiting for a callback to complete execution.
         *
         * @method isRunning
         * @return {Boolean} true if queue is waiting for a
         *                   from any initiated transactions
         */
        isRunning : function () {
            return !!this._running;
        },

        /**
         * Default functionality for the &quot;execute&quot; event.  Executes the
         * callback function
         *
         * @method _defExecFn
         * @param e {Event} the event object
         * @protected
         */
        _defExecFn : function (e) {
            e.callback();
        },

        /**
         * Add any number of callbacks to the end of the queue. Callbacks may be
         * provided as functions or objects.
         *
         * @method add
         * @param callback* {Function|Object} 0..n callbacks
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        add : function () {
            this.fire('add', { callbacks: Y.Array(arguments,0,true) });

            return this;
        },

        /**
         * Default functionality for the &quot;add&quot; event.  Adds the callbacks
         * in the event facade to the queue. Callbacks successfully added to the
         * queue are present in the event's <code>added</code> property in the
         * after phase.
         *
         * @method _defAddFn
         * @param e {Event} the event object
         * @protected
         */
        _defAddFn : function(e) {
            var _q = this._q,
                added = [];

            Y.Array.each(e.callbacks, function (c) {
                if (isObject(c)) {
                    _q.push(c);
                    added.push(c);
                }
            });

            e.added = added;
        },

        /**
         * Pause the execution of the queue after the execution of the current
         * callback completes.  If called from code outside of a queued callback,
         * clears the timeout for the pending callback. Paused queue can be
         * restarted with q.run()
         *
         * @method pause
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        pause: function () {
            if (isObject(this._running)) {
                this._running.cancel();
            }

            this._running = false;

            return this;
        },

        /**
         * Stop and clear the queue after the current execution of the
         * current callback completes.
         *
         * @method stop
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        stop : function () {
            this._q = [];

            return this.pause();
        },

        /**
         * Returns the current index of a callback.  Pass in either the id or
         * callback function from getCallback.
         *
         * @method indexOf
         * @param callback {String|Function} the callback or its specified id
         * @return {Number} index of the callback or -1 if not found
         */
        indexOf : function (callback) {
            var i = 0, len = this._q.length, c;

            for (; i < len; ++i) {
                c = this._q[i];
                if (c === callback || c.id === callback) {
                    return i;
                }
            }

            return -1;
        },

        /**
         * Retrieve a callback by its id.  Useful to modify the configuration
         * while the queue is running.
         *
         * @method getCallback
         * @param id {String} the id assigned to the callback
         * @return {Object} the callback object
         */
        getCallback : function (id) {
            var i = this.indexOf(id);

            return (i > -1) ? this._q[i] : null;
        },

        /**
         * Promotes the named callback to the top of the queue. If a callback is
         * currently executing or looping (via until or iterations), the promotion
         * is scheduled to occur after the current callback has completed.
         *
         * @method promote
         * @param callback {String|Object} the callback object or a callback's id
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        promote : function (callback) {
            var payload = { callback : callback },e;

            if (this.isRunning()) {
                e = this.after(SHIFT, function () {
                        this.fire(PROMOTE, payload);
                        e.detach();
                    }, this);
            } else {
                this.fire(PROMOTE, payload);
            }

            return this;
        },

        /**
         * <p>Default functionality for the &quot;promote&quot; event.  Promotes the
         * named callback to the head of the queue.</p>
         *
         * <p>The event object will contain a property &quot;callback&quot;, which
         * holds the id of a callback or the callback object itself.</p>
         *
         * @method _defPromoteFn
         * @param e {Event} the custom event
         * @protected
         */
        _defPromoteFn : function (e) {
            var i = this.indexOf(e.callback),
                promoted = (i > -1) ? this._q.splice(i,1)[0] : null;

            e.promoted = promoted;

            if (promoted) {
                this._q.unshift(promoted);
            }
        },

        /**
         * Removes the callback from the queue.  If the queue is active, the
         * removal is scheduled to occur after the current callback has completed.
         *
         * @method remove
         * @param callback {String|Object} the callback object or a callback's id
         * @return {AsyncQueue} the AsyncQueue instance
         * @chainable
         */
        remove : function (callback) {
            var payload = { callback : callback },e;

            // Can't return the removed callback because of the deferral until
            // current callback is complete
            if (this.isRunning()) {
                e = this.after(SHIFT, function () {
                        this.fire(REMOVE, payload);
                        e.detach();
                    },this);
            } else {
                this.fire(REMOVE, payload);
            }

            return this;
        },

        /**
         * <p>Default functionality for the &quot;remove&quot; event.  Removes the
         * callback from the queue.</p>
         *
         * <p>The event object will contain a property &quot;callback&quot;, which
         * holds the id of a callback or the callback object itself.</p>
         *
         * @method _defRemoveFn
         * @param e {Event} the custom event
         * @protected
         */
        _defRemoveFn : function (e) {
            var i = this.indexOf(e.callback);

            e.removed = (i > -1) ? this._q.splice(i,1)[0] : null;
        },

        /**
         * Returns the number of callbacks in the queue.
         *
         * @method size
         * @return {Number}
         */
        size : function () {
            // next() flushes callbacks that have met their until() criteria and
            // therefore shouldn't count since they wouldn't execute anyway.
            if (!this.isRunning()) {
                this.next();
            }

            return this._q.length;
        }
    });

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