Sys.UI.Behavior

            Type.registerNamespace('Samples');
            Samples.EmptyBehavior = function(element) {
            Samples.EmptyBehavior.initializeBase(this, [element]);
            }
            Samples.EmptyBehavior.prototype = {
            initialize : function() {
            Samples.EmptyBehavior.callBaseMethod(this, 'initialize');
            },
            dispose : function() {
            Samples.EmptyBehavior.callBaseMethod(this, 'dispose');
            }
            }
            Samples.EmptyBehavior.registerClass('Samples.EmptyBehavior',
            Sys.UI.Behavior);

            //Creating behavior

            $create(Samples.EmptyBehavior, {'name':'myEmptyBehavior'}, {}, {},
            $get('elementID'));

            //accessing behaviors
            var instance = $find('someElement$myEmptyBehavior');
            //or
            var emptyBehaviorInstance = $get('someElement').myEmptyBehavior;
            

            Type.registerNamespace('Samples');

            // Samples.FormattingBehavior class.
            Samples.FormattingBehavior = function(element) {
            Samples.FormattingBehavior.initializeBase(this, [element]);

            // Fields.
            this._hoverCssClass = null;
            this._focusCssClass = null;
            this._currentCssClass = null;
            this._mouseOver = null;
            this._focus = null;
            }
            Samples.FormattingBehavior.prototype = {
            // Component lifecycle.
            initialize : function() {
            Samples.FormattingBehavior.callBaseMethod(this, 'initialize');
            //this is changing the
            //the behavior of the associated
            //element
            //get_element is inherit from parent.

            $addHandlers(this.get_element(),
            {
            mouseout:this._onMouseout,
            mouseover:this._onMouseover,
            focus:this._onFocus,
            blur:this._onBlur
            }, this);
            },

            dispose : function() {
            $clearHandlers(this.get_element());

            Samples.FormattingBehavior.callBaseMethod(this, 'dispose');
            },

            // Event handlers.
            _onMouseover : function() {
            this._mouseOver = true;
            this._setCssClass();
            },

            _onMouseout : function() {
            this._mouseOver = false;
            this._setCssClass();
            },

            _onFocus : function() {
            this._focus = true;
            this._setCssClass();
            },

            _onBlur : function() {
            this._focus = false;
            this._setCssClass();
            },

            // Helper method.
            _setCssClass : function() {
            if (this._currentCssClass) {
            Sys.UI.DomElement.removeCssClass(this._element,
            this._currentCssClass);
            this._currentCssClass = null;
            }

            if (this._error) {
            this._currentCssClass = this._errorCssClass;
            }
            else if (this._focus) {
            this._currentCssClass = this._focusCssClass;
            }
            else if (this._mouseOver) {
            this._currentCssClass = this._hoverCssClass;
            }

            if (this._currentCssClass) {
            Sys.UI.DomElement.addCssClass(this._element,
            this._currentCssClass);
            }
            },

            // Properties.
            get_hoverCssClass : function() {
            return this._hoverCssClass;
            },

            set_hoverCssClass : function(value) {
            this._hoverCssClass = value;
            },

            get_focusCssClass : function() {
            return this._focusCssClass;
            },

            set_focusCssClass : function(value) {
            this._focusCssClass = value;
            }
            }
            // Inherit from Sys.UI.Behavior.
            Samples.FormattingBehavior.registerClass('Samples.FormattingBehavior', Sys.UI.Behavior);


            //add the client side we attached the behavior to element
            Sys.Application.add_init(pageInit);

            function pageInit(sender, e) {
            // Attach the FormattingBehavior to the txtName textbox.
            $create(Samples.FormattingBehavior,
            {'hoverCssClass':'field_hover', 'focusCssClass':'field_focus'},
            {}, {}, $get('Name'));

            // Attach the FormattingBehavior to the txtLastName textbox.
            $create(Samples.FormattingBehavior,
            {'hoverCssClass':'field_hover', 'focusCssClass':'field_focus'},
            {}, {}, $get('LastName'));
            }
            //$create function will automatically call the initialize method.