RadMultiSelect for ASP.NET AJAX is based on the Kendo UI MultiSelect Widget. Thus, it exposes the Client-side API and methods offered by the widget and mainly provides a wrapper and API for working with the MultiSelect on the server.
        You can get Client-side Object Reference to the MultiSelect control in order to use its API like this: 
        
        
var RadMultiSelectObject = $find("<%=RadMultiSelect1.ClientID %>");
        
    
    
        The most commonly used RadMultiSelect client-side methods are:
    
    
        - 
            set_enabled—Enables or disables the widget.
        
 
        - 
            set_readOnly—Toggles the readonly state of the widget. When the widget is readonly it doesn't allow user input.
        
 
        - 
            open—Opens the popup.
        
 
        - 
            close—Closes the widget popup.
        
 
        - 
            toggle—Opens or closes the widget popup.
        
 
        - 
            search—Searches the data source for the provided value and displays any matches as suggestions.
        
 
        - 
            get_value and set_value—Gets or sets the value of the MultiSelect.
        
 
    
    You can find the full client-side API of the control in the RadMultiSelect Client-side API documentation article.
    
    
        Get Client-side Object Reference to the Kendo MultiSelect widget in order to use its API
    
    
        There are two ways to get a reference to the Kendo MultiSelect widget in order to use its API:
        
            - 
                Use the get_kendoWidget method the RadMultiSelect client-side object exposes. You can get the RadMultiSelect object through the $find() MS AJAX method:
                
                var RadMultiSelectObject  = $find("<%=RadMultiSelect1.ClientID %>"); //the standard script control object
                var kendoMultiSelectObject = RadMultiSelectObject.get_kendoWidget(); //the Kendo widget
                
             
            - 
                Use the standard Kendo approach for getting the widget through the data-attributes of the DOM element:
                
                var kendoMultiSelectObject = $telerik.$("#<%=RadMultiSelect1.ClientID %>").data("kendoMultiSelect"); //the jQuery selector must get the RadMultiSelect1 select element