If I have an html page where the user selects a parameter being to my report is there any way to add an alert if a parameter wasn't select?

I kind of read that Javascript was used to add alerts, but I am not sure where. Can anyone help?

Thank you.

I've always used a snippet like this in the click event of the 'Run' button (or whatever runs the report). It will exit the function if the user hasn't selected a quarter, and it won't run the FEX.

if ((document.paramform.QTR.value=='0')) {
alert("Please select a QUARTER.");
return
}