Link drop-downs in JScript

I have no JScript experience whatsoever, and have been asked to provide 2 linked drop-down lists which must be in JScript.
Depending upon the contents of the 1st drop-down, I will limit the choices in the second. From the JScript help in VS.Net I have got as far as what is shown below. Pitiful, I know.

switch (parseInt(event.srcElement.returnValue, 10))
{ /* Selection 1 */
case 1:
window.alert('Item 1');
break;
/* Selection 2*/
case 2:
window.alert('Item 2');
break;
/* Selection 3*/
case 3:
window.alert('Item 3');
break;
/* Selection 4*/
case 4:
window.alert('Item 4');
break;
}

Thanks in advance.