How to set the value of an item after it is dynamically added to dropdownlist! /Use js to control the readonly attribute of the server dropdownlist and textfield

There are two ways to write: The method of not using data sources
1 ):
Listitem mylistitem = new listitem ("text", "value ");
This. dropdownlist1.items. Add (mylistitem );
2 ):
This. dropdownlist1.items. Add ("text1 ");
This. dropdownlist1.items. findbytext ("text1"). value = "value1 ";

3): Use js to control the readonly attributes of the server dropdownlist and textfield.
<Asp: dropdownlist id = "ddlcardtype" runat = "server"> </ASP: dropdownlist>
Readonly = disabled
Document. getelementbyid ("<% = ddlcardtype. clientid %>"). Disabled = "disabled ";
Document. getelementbyid ("<% = txtlastfour. clientid %>"). Disabled = "disabled ";