# Yahoo! UI Library

### attribute 3.1.1

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        /**
         * The attribute module provides an augmentable Attribute implementation, which
         * adds configurable attributes and attribute change events to the class being
         * augmented. It also provides a State class, which is used internally by Attribute,
         * but can also be used independently to provide a name/property/value data structure to
         * store state.
         *
         * @module attribute
         */

        /**
         * The attribute-base submodule provides core attribute handling support, with everything
         * aside from complex attribute handling in the provider's constructor.
         *
         * @module attribute
         * @submodule attribute-base
         */
        var O = Y.Object,
            Lang = Y.Lang,
            EventTarget = Y.EventTarget,

            DOT = ".",
            CHANGE = "Change",

            // Externally configurable props
            GETTER = "getter",
            SETTER = "setter",
            READ_ONLY = "readOnly",
            WRITE_ONCE = "writeOnce",
            INIT_ONLY = "initOnly",
            VALIDATOR = "validator",
            VALUE = "value",
            VALUE_FN = "valueFn",
            BROADCAST = "broadcast",
            LAZY_ADD = "lazyAdd",
            BYPASS_PROXY = "_bypassProxy",

            // Used for internal state management
            ADDED = "added",
            INITIALIZING = "initializing",
            INIT_VALUE = "initValue",
            PUBLISHED = "published",
            DEF_VALUE = "defaultValue",
            LAZY = "lazy",
            IS_LAZY_ADD = "isLazyAdd",

            INVALID_VALUE,

            MODIFIABLE = {};

            // Properties which can be changed after the attribute has been added.
            MODIFIABLE[READ_ONLY] = 1;
            MODIFIABLE[WRITE_ONCE] = 1;
            MODIFIABLE[GETTER] = 1;
            MODIFIABLE[BROADCAST] = 1;

        /**
         * <p>
         * Attribute provides configurable attribute support along with attribute change events. It is designed to be
         * augmented on to a host class, and provides the host with the ability to configure attributes to store and retrieve state,
         * along with attribute change events.
         * </p>
         * <p>For example, attributes added to the host can be configured:</p>
         * <ul>
         *     <li>As read only.</li>
         *     <li>As write once.</li>
         *     <li>With a setter function, which can be used to manipulate
         *     values passed to Attribute's <a href="#method_set">set</a> method, before they are stored.</li>
         *     <li>With a getter function, which can be used to manipulate stored values,
         *     before they are returned by Attribute's <a href="#method_get">get</a> method.</li>
         *     <li>With a validator function, to validate values before they are stored.</li>
         * </ul>
         *
         * <p>See the <a href="#method_addAttr">addAttr</a> method, for the complete set of configuration
         * options available for attributes</p>.
         *
         * <p><strong>NOTE:</strong> Most implementations will be better off extending the <a href="Base.html">Base</a> class,
         * instead of augmenting Attribute directly. Base augments Attribute and will handle the initial configuration
         * of attributes for derived classes, accounting for values passed into the constructor.</p>
         *
         * @class Attribute
         * @uses EventTarget
         */
        function Attribute() {
            Y.log('Attribute constructor called', 'info', 'attribute');

            var host = this, // help compression
                attrs = this.constructor.ATTRS,
                Base = Y.Base;

            // Perf tweak - avoid creating event literals if not required.
            host._ATTR_E_FACADE = {};

            EventTarget.call(host, {emitFacade:true});

            // _conf maintained for backwards compat
            host._conf = host._state = new Y.State();

            host._stateProxy = host._stateProxy || null;
            host._requireAddAttr = host._requireAddAttr || false;

            // ATTRS support for Node, which is not Base based
            if ( attrs && !(Base && host instanceof Base)) {
                host.addAttrs(this._protectAttrs(attrs));
            }
        }

        /**
         * <p>The value to return from an attribute setter in order to prevent the set from going through.</p>
         *
         * <p>You can return this value from your setter if you wish to combine validator and setter
         * functionality into a single setter function, which either returns the massaged value to be stored or
         * Attribute.INVALID_VALUE to prevent invalid values from being stored.</p>
         *
         * @property Attribute.INVALID_VALUE
         * @type Object
         * @static
         * @final
         */
        Attribute.INVALID_VALUE = {};
        INVALID_VALUE = Attribute.INVALID_VALUE;

        /**
         * The list of properties which can be configured for
         * each attribute (e.g. setter, getter, writeOnce etc.).
         *
         * This property is used internally as a whitelist for faster
         * Y.mix operations.
         *
         * @property Attribute._ATTR_CFG
         * @type Array
         * @static
         * @protected
         */
        Attribute._ATTR_CFG = [SETTER, GETTER, VALIDATOR, VALUE, VALUE_FN, WRITE_ONCE, READ_ONLY, LAZY_ADD, BROADCAST, BYPASS_PROXY];

        Attribute.prototype = {
            /**
             * <p>
             * Adds an attribute with the provided configuration to the host object.
             * </p>
             * <p>
             * The config argument object supports the following properties:
             * </p>
             *
             * <dl>
             *    <dt>value &#60;Any&#62;</dt>
             *    <dd>The initial value to set on the attribute</dd>
             *
             *    <dt>valueFn &#60;Function | String&#62;</dt>
             *    <dd>
             *    <p>A function, which will return the initial value to set on the attribute. This is useful
             *    for cases where the attribute configuration is defined statically, but needs to
             *    reference the host instance ("this") to obtain an initial value.
             *    If defined, valueFn has precedence over the value property.</p>
             *
             *    <p>valueFn can also be set to a string, representing the name of the instance method to be used to retrieve the value.</p>
             *    </dd>
             *
             *    <dt>readOnly &#60;boolean&#62;</dt>
             *    <dd>Whether or not the attribute is read only. Attributes having readOnly set to true
             *        cannot be modified by invoking the set method.</dd>
             *
             *    <dt>writeOnce &#60;boolean&#62;</dt>
             *    <dd>Whether or not the attribute is "write once". Attributes having writeOnce set to true,
             *        can only have their values set once, be it through the default configuration,
             *        constructor configuration arguments, or by invoking set.</dd>
             *
             *    <dt>setter &#60;Function | String&#62;</dt>
             *    <dd>
             *    <p>The setter function used to massage or normalize the value passed to the set method for the attribute.
             *    The value returned by the setter will be the final stored value. Returning
             *    <a href="#property_Attribute.INVALID_VALUE">Attribute.INVALID_VALUE</a>, from the setter will prevent
             *    the value from being stored.
             *    </p>
             *
             *    <p>setter can also be set to a string, representing the name of the instance method to be used as the setter function.</p>
             *    </dd>
             *
             *    <dt>getter &#60;Function | String&#62;</dt>
             *    <dd>
             *    <p>
             *    The getter function used to massage or normalize the value returned by the get method for the attribute.
             *    The value returned by the getter function is the value which will be returned to the user when they
             *    invoke get.
             *    </p>
             *
             *    <p>getter can also be set to a string, representing the name of the instance method to be used as the getter function.</p>
             *    </dd>
             *
             *    <dt>validator &#60;Function | String&#62;</dt>
             *    <dd>
             *    <p>
             *    The validator function invoked prior to setting the stored value. Returning
             *    false from the validator function will prevent the value from being stored.
             *    </p>
             *
             *    <p>validator can also be set to a string, representing the name of the instance method to be used as the validator function.</p>
             *    </dd>
             *
             *    <dt>broadcast &#60;int&#62;</dt>
             *    <dd>If and how attribute change events for this attribute should be broadcast. See CustomEvent's <a href="CustomEvent.html#property_broadcast">broadcast</a> property for
             *    valid values. By default attribute change events are not broadcast.</dd>
             *
             *    <dt>lazyAdd &#60;boolean&#62;</dt>
             *    <dd>Whether or not to delay initialization of the attribute until the first call to get/set it.
             *    This flag can be used to over-ride lazy initialization on a per attribute basis, when adding multiple attributes through
             *    the <a href="#method_addAttrs">addAttrs</a> method.</dd>
             *
             * </dl>
             *
             * <p>The setter, getter and validator are invoked with the value and name passed in as the first and second arguments, and with
             * the context ("this") set to the host object.</p>
             *
             * <p>Configuration properties outside of the list mentioned above are considered private properties used internally by attribute, and are not intended for public use.</p>
             *
             * @method addAttr
             *
             * @param {String} name The name of the attribute.
             * @param {Object} config An object with attribute configuration property/value pairs, specifying the configuration for the attribute.
             *
             * <p>
             * <strong>NOTE:</strong> The configuration object is modified when adding an attribute, so if you need
             * to protect the original values, you will need to merge the object.
             * </p>
             *
             * @param {boolean} lazy (optional) Whether or not to add this attribute lazily (on the first call to get/set).
             *
             * @return {Object} A reference to the host object.
             *
             * @chainable
             */
            addAttr: function(name, config, lazy) {

                Y.log('Adding attribute: ' + name, 'info', 'attribute');

                var host = this, // help compression
                    state = host._state,
                    value,
                    hasValue;

                lazy = (LAZY_ADD in config) ? config[LAZY_ADD] : lazy;

                if (lazy && !host.attrAdded(name)) {
                    state.add(name, LAZY, config || {});
                    state.add(name, ADDED, true);
                } else {

                    if (host.attrAdded(name) && !state.get(name, IS_LAZY_ADD)) { Y.log('Attribute: ' + name + ' already exists. Cannot add it again without removing it first', 'warn', 'attribute'); }

                    if (!host.attrAdded(name) || state.get(name, IS_LAZY_ADD)) {

                        config = config || {};

                        hasValue = (VALUE in config);

                        if (config.readOnly && !hasValue) { Y.log('readOnly attribute: ' + name + ', added without an initial value. Value will be set on initial call to set', 'warn', 'attribute');}

                        if(hasValue) {
                            // We'll go through set, don't want to set value in config directly
                            value = config.value;
                            delete config.value;
                        }

                        config.added = true;
                        config.initializing = true;

                        state.addAll(name, config);

                        if (hasValue) {
                            // Go through set, so that raw values get normalized/validated
                            host.set(name, value);
                        }

                        state.remove(name, INITIALIZING);
                    }
                }

                return host;
            },

            /**
             * Checks if the given attribute has been added to the host
             *
             * @method attrAdded
             * @param {String} name The name of the attribute to check.
             * @return {boolean} true if an attribute with the given name has been added, false if it hasn't. This method will return true for lazily added attributes.
             */
            attrAdded: function(name) {
                return !!this._state.get(name, ADDED);
            },

            /**
             * Updates the configuration of an attribute which has already been added.
             * <p>
             * The properties which can be modified through this interface are limited
             * to the following subset of attributes, which can be safely modified
             * after a value has already been set on the attribute: readOnly, writeOnce,
             * broadcast and getter.
             * </p>
             * @method modifyAttr
             * @param {String} name The name of the attribute whose configuration is to be updated.
             * @param {Object} config An object with configuration property/value pairs, specifying the configuration properties to modify.
             */
            modifyAttr: function(name, config) {
                var host = this, // help compression
                    prop, state;

                if (host.attrAdded(name)) {

                    if (host._isLazyAttr(name)) {
                        host._addLazyAttr(name);
                    }

                    state = host._state;
                    for (prop in config) {
                        if (MODIFIABLE[prop] && config.hasOwnProperty(prop)) {
                            state.add(name, prop, config[prop]);

                            // If we reconfigured broadcast, need to republish
                            if (prop === BROADCAST) {
                                state.remove(name, PUBLISHED);
                            }
                        }
                    }
                }

                if (!host.attrAdded(name)) {Y.log('Attribute modifyAttr:' + name + ' has not been added. Use addAttr to add the attribute', 'warn', 'attribute');}
            },

            /**
             * Removes an attribute from the host object
             *
             * @method removeAttr
             * @param {String} name The name of the attribute to be removed.
             */
            removeAttr: function(name) {
                this._state.removeAll(name);
            },

            /**
             * Returns the current value of the attribute. If the attribute
             * has been configured with a 'getter' function, this method will delegate
             * to the 'getter' to obtain the value of the attribute.
             *
             * @method get
             *
             * @param {String} name The name of the attribute. If the value of the attribute is an Object,
             * dot notation can be used to obtain the value of a property of the object (e.g. <code>get("x.y.z")</code>)
             *
             * @return {Any} The value of the attribute
             */
            get : function(name) {
                return this._getAttr(name);
            },

            /**
             * Checks whether or not the attribute is one which has been
             * added lazily and still requires initialization.
             *
             * @method _isLazyAttr
             * @private
             * @param {String} name The name of the attribute
             * @return {boolean} true if it's a lazily added attribute, false otherwise.
             */
            _isLazyAttr: function(name) {
                return this._state.get(name, LAZY);
            },

            /**
             * Finishes initializing an attribute which has been lazily added.
             *
             * @method _addLazyAttr
             * @private
             * @param {Object} name The name of the attribute
             */
            _addLazyAttr: function(name) {
                var state = this._state,
                    lazyCfg = state.get(name, LAZY);

                state.add(name, IS_LAZY_ADD, true);
                state.remove(name, LAZY);
                this.addAttr(name, lazyCfg);
            },

            /**
             * Sets the value of an attribute.
             *
             * @method set
             * @chainable
             *
             * @param {String} name The name of the attribute. If the
             * current value of the attribute is an Object, dot notation can be used
             * to set the value of a property within the object (e.g. <code>set("x.y.z", 5)</code>).
             *
             * @param {Any} value The value to set the attribute to.
             *
             * @param {Object} opts (Optional) Optional event data to be mixed into
             * the event facade passed to subscribers of the attribute's change event. This
             * can be used as a flexible way to identify the source of a call to set, allowing
             * the developer to distinguish between set called internally by the host, vs.
             * set called externally by the application developer.
             *
             * @return {Object} A reference to the host object.
             */
            set : function(name, val, opts) {
                return this._setAttr(name, val, opts);
            },

            /**
             * Resets the attribute (or all attributes) to its initial value, as long as
             * the attribute is not readOnly, or writeOnce.
             *
             * @method reset
             * @param {String} name Optional. The name of the attribute to reset.  If omitted, all attributes are reset.
             * @return {Object} A reference to the host object.
             * @chainable
             */
            reset : function(name) {
                var host = this,  // help compression
                    added;

                if (name) {
                    if (host._isLazyAttr(name)) {
                        host._addLazyAttr(name);
                    }
                    host.set(name, host._state.get(name, INIT_VALUE));
                } else {
                    added = host._state.data.added;
                    Y.each(added, function(v, n) {
                        host.reset(n);
                    }, host);
                }
                return host;
            },

            /**
             * Allows setting of readOnly/writeOnce attributes. See <a href="#method_set">set</a> for argument details.
             *
             * @method _set
             * @protected
             * @chainable
             *
             * @param {String} name The name of the attribute.
             * @param {Any} val The value to set the attribute to.
             * @param {Object} opts (Optional) Optional event data to be mixed into
             * the event facade passed to subscribers of the attribute's change event.
             * @return {Object} A reference to the host object.
             */
            _set : function(name, val, opts) {
                return this._setAttr(name, val, opts, true);
            },

            /**
             * Provides the common implementation for the public get method,
             * allowing Attribute hosts to over-ride either method.
             *
             * See <a href="#method_get">get</a> for argument details.
             *
             * @method _getAttr
             * @protected
             * @chainable
             *
             * @param {String} name The name of the attribute.
             * @return {Any} The value of the attribute.
             */
            _getAttr : function(name) {
                var host = this, // help compression
                    fullName = name,
                    state = host._state,
                    path,
                    getter,
                    val,
                    cfg;

                if (name.indexOf(DOT) !== -1) {
                    path = name.split(DOT);
                    name = path.shift();
                }

                // On Demand - Should be rare - handles out of order valueFn references
                if (host._tCfgs && host._tCfgs[name]) {
                    cfg = {};
                    cfg[name] = host._tCfgs[name];
                    delete host._tCfgs[name];
                    host._addAttrs(cfg, host._tVals);
                }

                // Lazy Init
                if (host._isLazyAttr(name)) {
                    host._addLazyAttr(name);
                }

                val = host._getStateVal(name);
                getter = state.get(name, GETTER);

                if (getter && !getter.call) {
                    getter = this[getter];
                }

                val = (getter) ? getter.call(host, val, fullName) : val;
                val = (path) ? O.getValue(val, path) : val;

                return val;
            },

            /**
             * Provides the common implementation for the public set and protected _set methods.
             *
             * See <a href="#method_set">set</a> for argument details.
             *
             * @method _setAttr
             * @protected
             * @chainable
             *
             * @param {String} name The name of the attribute.
             * @param {Any} value The value to set the attribute to.
             * @param {Object} opts (Optional) Optional event data to be mixed into
             * the event facade passed to subscribers of the attribute's change event.
             * @param {boolean} force If true, allows the caller to set values for
             * readOnly or writeOnce attributes which have already been set.
             *
             * @return {Object} A reference to the host object.
             */
            _setAttr : function(name, val, opts, force) {
                var allowSet = true,
                    state = this._state,
                    stateProxy = this._stateProxy,
                    data = state.data,
                    initialSet,
                    strPath,
                    path,
                    currVal,
                    writeOnce,
                    initializing;

                if (name.indexOf(DOT) !== -1) {
                    strPath = name;
                    path = name.split(DOT);
                    name = path.shift();
                }

                if (this._isLazyAttr(name)) {
                    this._addLazyAttr(name);
                }

                initialSet = (!data.value || !(name in data.value));

                if (stateProxy && name in stateProxy && !this._state.get(name, BYPASS_PROXY)) {
                    // TODO: Value is always set for proxy. Can we do any better? Maybe take a snapshot as the initial value for the first call to set?
                    initialSet = false;
                }

                if (this._requireAddAttr && !this.attrAdded(name)) {
                    Y.log('Set attribute:' + name + ', aborted; Attribute is not configured', 'warn', 'attribute');
                } else {

                    writeOnce = state.get(name, WRITE_ONCE);
                    initializing = state.get(name, INITIALIZING);

                    if (!initialSet && !force) {

                        if (writeOnce) {
                            Y.log('Set attribute:' + name + ', aborted; Attribute is writeOnce', 'warn', 'attribute');
                            allowSet = false;
                        }

                        if (state.get(name, READ_ONLY)) {
                            Y.log('Set attribute:' + name + ', aborted; Attribute is readOnly', 'warn', 'attribute');
                            allowSet = false;
                        }
                    }

                    if (!initializing && !force && writeOnce === INIT_ONLY) {
                        Y.log('Set attribute:' + name + ', aborted; Attribute is writeOnce: "initOnly"', 'warn', 'attribute');
                        allowSet = false;
                    }

                    if (allowSet) {
                        // Don't need currVal if initialSet (might fail in custom getter if it always expects a non-undefined/non-null value)
                        if (!initialSet) {
                            currVal =  this.get(name);
                        }

                        if (path) {
                           val = O.setValue(Y.clone(currVal), path, val);

                           if (val === undefined) {
                               Y.log('Set attribute path:' + strPath + ', aborted; Path is invalid', 'warn', 'attribute');
                               allowSet = false;
                           }
                        }

                        if (allowSet) {
                            if (initializing) {
                                this._setAttrVal(name, strPath, currVal, val);
                            } else {
                                this._fireAttrChange(name, strPath, currVal, val, opts);
                            }
                        }
                    }
                }

                return this;
            },

            /**
             * Utility method to help setup the event payload and fire the attribute change event.
             *
             * @method _fireAttrChange
             * @private
             * @param {String} attrName The name of the attribute
             * @param {String} subAttrName The full path of the property being changed,
             * if this is a sub-attribute value being change. Otherwise null.
             * @param {Any} currVal The current value of the attribute
             * @param {Any} newVal The new value of the attribute
             * @param {Object} opts Any additional event data to mix into the attribute change event's event facade.
             */
            _fireAttrChange : function(attrName, subAttrName, currVal, newVal, opts) {
                var host = this,
                    eventName = attrName + CHANGE,
                    state = host._state,
                    facade;

                if (!state.get(attrName, PUBLISHED)) {
                    host.publish(eventName, {
                        queuable:false,
                        defaultTargetOnly: true,
                        defaultFn:host._defAttrChangeFn,
                        silent:true,
                        broadcast : state.get(attrName, BROADCAST)
                    });
                    state.add(attrName, PUBLISHED, true);
                }

                facade = (opts) ? Y.merge(opts) : host._ATTR_E_FACADE;

                facade.type = eventName;
                facade.attrName = attrName;
                facade.subAttrName = subAttrName;
                facade.prevVal = currVal;
                facade.newVal = newVal;

                host.fire(facade);
            },

            /**
             * Default function for attribute change events.
             *
             * @private
             * @method _defAttrChangeFn
             * @param {EventFacade} e The event object for attribute change events.
             */
            _defAttrChangeFn : function(e) {
                if (!this._setAttrVal(e.attrName, e.subAttrName, e.prevVal, e.newVal)) {
                    Y.log('State not updated and stopImmediatePropagation called for attribute: ' + e.attrName + ' , value:' + e.newVal, 'warn', 'attribute');
                    // Prevent "after" listeners from being invoked since nothing changed.
                    e.stopImmediatePropagation();
                } else {
                    e.newVal = this.get(e.attrName);
                }
            },

            /**
             * Gets the stored value for the attribute, from either the
             * internal state object, or the state proxy if it exits
             *
             * @method _getStateVal
             * @private
             * @param {String} name The name of the attribute
             * @return {Any} The stored value of the attribute
             */
            _getStateVal : function(name) {
                var stateProxy = this._stateProxy;
                return stateProxy && (name in stateProxy) && !this._state.get(name, BYPASS_PROXY) ? stateProxy[name] : this._state.get(name, VALUE);
            },

            /**
             * Sets the stored value for the attribute, in either the
             * internal state object, or the state proxy if it exits
             *
             * @method _setStateVal
             * @private
             * @param {String} name The name of the attribute
             * @param {Any} value The value of the attribute
             */
            _setStateVal : function(name, value) {
                var stateProxy = this._stateProxy;
                if (stateProxy && (name in stateProxy) && !this._state.get(name, BYPASS_PROXY)) {
                    stateProxy[name] = value;
                } else {
                    this._state.add(name, VALUE, value);
                }
            },

            /**
             * Updates the stored value of the attribute in the privately held State object,
             * if validation and setter passes.
             *
             * @method _setAttrVal
             * @private
             * @param {String} attrName The attribute name.
             * @param {String} subAttrName The sub-attribute name, if setting a sub-attribute property ("x.y.z").
             * @param {Any} prevVal The currently stored value of the attribute.
             * @param {Any} newVal The value which is going to be stored.
             *
             * @return {booolean} true if the new attribute value was stored, false if not.
             */
            _setAttrVal : function(attrName, subAttrName, prevVal, newVal) {

                var host = this,
                    allowSet = true,
                    state = host._state,

                    validator = state.get(attrName, VALIDATOR),
                    setter = state.get(attrName, SETTER),
                    initializing = state.get(attrName, INITIALIZING),
                    prevValRaw = this._getStateVal(attrName),

                    name = subAttrName || attrName,
                    retVal,
                    valid;

                if (validator) {
                    if (!validator.call) {
                        // Assume string - trying to keep critical path tight, so avoiding Lang check
                        validator = this[validator];
                    }
                    if (validator) {
                        valid = validator.call(host, newVal, name);

                        if (!valid && initializing) {
                            newVal = state.get(attrName, DEF_VALUE);
                            valid = true; // Assume it's valid, for perf.
                        }
                    }
                }

                if (!validator || valid) {
                    if (setter) {
                        if (!setter.call) {
                            // Assume string - trying to keep critical path tight, so avoiding Lang check
                            setter = this[setter];
                        }
                        if (setter) {
                            retVal = setter.call(host, newVal, name);

                            if (retVal === INVALID_VALUE) {
                                Y.log('Attribute: ' + attrName + ', setter returned Attribute.INVALID_VALUE for value:' + newVal, 'warn', 'attribute');
                                allowSet = false;
                            } else if (retVal !== undefined){
                                Y.log('Attribute: ' + attrName + ', raw value: ' + newVal + ' modified by setter to:' + retVal, 'info', 'attribute');
                                newVal = retVal;
                            }
                        }
                    }

                    if (allowSet) {
                        if(!subAttrName && (newVal === prevValRaw) && !Lang.isObject(newVal)) {
                            Y.log('Attribute: ' + attrName + ', value unchanged:' + newVal, 'warn', 'attribute');
                            allowSet = false;
                        } else {
                            // Store value
                            if (state.get(attrName, INIT_VALUE) === undefined) {
                                state.add(attrName, INIT_VALUE, newVal);
                            }
                            host._setStateVal(attrName, newVal);
                        }
                    }

                } else {
                    Y.log('Attribute:' + attrName + ', Validation failed for value:' + newVal, 'warn', 'attribute');
                    allowSet = false;
                }

                return allowSet;
            },

            /**
             * Sets multiple attribute values.
             *
             * @method setAttrs
             * @param {Object} attrs  An object with attributes name/value pairs.
             * @return {Object} A reference to the host object.
             * @chainable
             */
            setAttrs : function(attrs, opts) {
                return this._setAttrs(attrs, opts);
            },

            /**
             * Implementation behind the public setAttrs method, to set multiple attribute values.
             *
             * @method _setAttrs
             * @protected
             * @param {Object} attrs  An object with attributes name/value pairs.
             * @return {Object} A reference to the host object.
             * @chainable
             */
            _setAttrs : function(attrs, opts) {
                for (var attr in attrs) {
                    if ( attrs.hasOwnProperty(attr) ) {
                        this.set(attr, attrs[attr]);
                    }
                }
                return this;
            },

            /**
             * Gets multiple attribute values.
             *
             * @method getAttrs
             * @param {Array | boolean} attrs Optional. An array of attribute names. If omitted, all attribute values are
             * returned. If set to true, all attributes modified from their initial values are returned.
             * @return {Object} An object with attribute name/value pairs.
             */
            getAttrs : function(attrs) {
                return this._getAttrs(attrs);
            },

            /**
             * Implementation behind the public getAttrs method, to get multiple attribute values.
             *
             * @method _getAttrs
             * @protected
             * @param {Array | boolean} attrs Optional. An array of attribute names. If omitted, all attribute values are
             * returned. If set to true, all attributes modified from their initial values are returned.
             * @return {Object} An object with attribute name/value pairs.
             */
            _getAttrs : function(attrs) {
                var host = this,
                    o = {},
                    i, l, attr, val,
                    modifiedOnly = (attrs === true);

                attrs = (attrs && !modifiedOnly) ? attrs : O.keys(host._state.data.added);

                for (i = 0, l = attrs.length; i < l; i++) {
                    // Go through get, to honor cloning/normalization
                    attr = attrs[i];
                    val = host.get(attr);

                    if (!modifiedOnly || host._getStateVal(attr) != host._state.get(attr, INIT_VALUE)) {
                        o[attr] = host.get(attr);
                    }
                }

                return o;
            },

            /**
             * Configures a group of attributes, and sets initial values.
             *
             * <p>
             * <strong>NOTE:</strong> This method does not isolate the configuration object by merging/cloning.
             * The caller is responsible for merging/cloning the configuration object if required.
             * </p>
             *
             * @method addAttrs
             * @chainable
             *
             * @param {Object} cfgs An object with attribute name/configuration pairs.
             * @param {Object} values An object with attribute name/value pairs, defining the initial values to apply.
             * Values defined in the cfgs argument will be over-written by values in this argument unless defined as read only.
             * @param {boolean} lazy Whether or not to delay the intialization of these attributes until the first call to get/set.
             * Individual attributes can over-ride this behavior by defining a lazyAdd configuration property in their configuration.
             * See <a href="#method_addAttr">addAttr</a>.
             *
             * @return {Object} A reference to the host object.
             */
            addAttrs : function(cfgs, values, lazy) {
                var host = this; // help compression
                if (cfgs) {
                    host._tCfgs = cfgs;
                    host._tVals = host._normAttrVals(values);
                    host._addAttrs(cfgs, host._tVals, lazy);
                    host._tCfgs = host._tVals = null;
                }

                return host;
            },

            /**
             * Implementation behind the public addAttrs method.
             *
             * This method is invoked directly by get if it encounters a scenario
             * in which an attribute's valueFn attempts to obtain the
             * value an attribute in the same group of attributes, which has not yet
             * been added (on demand initialization).
             *
             * @method _addAttrs
             * @private
             * @param {Object} cfgs An object with attribute name/configuration pairs.
             * @param {Object} values An object with attribute name/value pairs, defining the initial values to apply.
             * Values defined in the cfgs argument will be over-written by values in this argument unless defined as read only.
             * @param {boolean} lazy Whether or not to delay the intialization of these attributes until the first call to get/set.
             * Individual attributes can over-ride this behavior by defining a lazyAdd configuration property in their configuration.
             * See <a href="#method_addAttr">addAttr</a>.
             */
            _addAttrs : function(cfgs, values, lazy) {
                var host = this, // help compression
                    attr,
                    attrCfg,
                    value;

                for (attr in cfgs) {
                    if (cfgs.hasOwnProperty(attr)) {

                        // Not Merging. Caller is responsible for isolating configs
                        attrCfg = cfgs[attr];
                        attrCfg.defaultValue = attrCfg.value;

                        // Handle simple, complex and user values, accounting for read-only
                        value = host._getAttrInitVal(attr, attrCfg, host._tVals);

                        if (value !== undefined) {
                            attrCfg.value = value;
                        }

                        if (host._tCfgs[attr]) {
                            delete host._tCfgs[attr];
                        }

                        host.addAttr(attr, attrCfg, lazy);
                    }
                }
            },

            /**
             * Utility method to protect an attribute configuration
             * hash, by merging the entire object and the individual
             * attr config objects.
             *
             * @method _protectAttrs
             * @protected
             * @param {Object} attrs A hash of attribute to configuration object pairs.
             * @return {Object} A protected version of the attrs argument.
             */
            _protectAttrs : function(attrs) {
                if (attrs) {
                    attrs = Y.merge(attrs);
                    for (var attr in attrs) {
                        if (attrs.hasOwnProperty(attr)) {
                            attrs[attr] = Y.merge(attrs[attr]);
                        }
                    }
                }
                return attrs;
            },

            /**
             * Utility method to normalize attribute values. The base implementation
             * simply merges the hash to protect the original.
             *
             * @method _normAttrVals
             * @param {Object} valueHash An object with attribute name/value pairs
             *
             * @return {Object}
             *
             * @private
             */
            _normAttrVals : function(valueHash) {
                return (valueHash) ? Y.merge(valueHash) : null;
            },

            /**
             * Returns the initial value of the given attribute from
             * either the default configuration provided, or the
             * over-ridden value if it exists in the set of initValues
             * provided and the attribute is not read-only.
             *
             * @param {String} attr The name of the attribute
             * @param {Object} cfg The attribute configuration object
             * @param {Object} initValues The object with simple and complex attribute name/value pairs returned from _normAttrVals
             *
             * @return {Any} The initial value of the attribute.
             *
             * @method _getAttrInitVal
             * @private
             */
            _getAttrInitVal : function(attr, cfg, initValues) {
                var val, valFn;
                // init value is provided by the user if it exists, else, provided by the config
                if (!cfg[READ_ONLY] && initValues && initValues.hasOwnProperty(attr)) {
                    val = initValues[attr];
                } else {
                    val = cfg[VALUE];
                    valFn = cfg[VALUE_FN];

                    if (valFn) {
                        if (!valFn.call) {
                            valFn = this[valFn];
                        }
                        if (valFn) {
                            val = valFn.call(this);
                        }
                    }
                }

                Y.log('initValue for ' + attr + ':' + val, 'info', 'attribute');

                return val;
            }
        };

        // Basic prototype augment - no lazy constructor invocation.
        Y.mix(Attribute, EventTarget, false, null, 1);

        Y.Attribute = Attribute;

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