Hello,

Regrettably, it is not supported to execute custom javascript with standard redirection behavior.

You would need to excute custom javascript code and then redirect users using javascript window.location. So, let's assume the following javascript function:

function myWindowOpen()
{
 alert("hello");
 window.location = "<url>";
 return false;
}
</script> 

You can place the function in CMSDesk -> Content -> select page with menu in tree -> Design -> Configuration of menu web part -> Content before field.

And than you call myWindowOpen() function in Javascript command property of a given document:

Javascript command: myWindowOpen();

Best regards,
Michal Legen