Use "debugger" word in jscript/vbscript code. Run project in debug mode. That will cause stop on that point and will allow to run project in step (f10) mode. All variables could be seen and added in watch windows of VS.

For example you have following code

<script>
function clientvalidate(source, args){
var dropdown =
document.getElementById(source.controltovalidate);
if (dropdown.selectedindex == 0){
args.IsValid = false;
} else {
args.IsValid = true;
}
}
</script>

to debug it in run time add debugger keyword.
See the following code

<script>
function clientvalidate(source, args){
debugger;
var dropdown =
document.getElementById(source.controltovalidate);
if (dropdown.selectedindex == 0){
args.IsValid = false;
} else {
args.IsValid = true;
}
}
</script>
run project in VS with debug mode (F5).


When the JavaScript interpreter reaches this keyword (debugger), it halts execution and returns control to the IDE (VS).

You can use F10, F11, F5, watch, add watch as you usually debugging your codebehind.


Thanks

Vladimir