dynamic text for checkbox prompt

[Arumugam]

Hi,

    I have placed the text box and applied the render variable for the same.Whenever the user selects the value in the checkbox value prompt,the text box above the prompt will display the text . when the parameter value(checkbox prompt) is null ,it wont show anything.It is working only when I click on refresh/submit button (onchange event).How to achieve the same functionality through javascript?