I tried below script in my PDI and it works for me.

function onChange(control, oldValue, newValue, isLoading) {
   if (isLoading || newValue == '') {
      return;
   }
if (newValue=='admin'){
	alert('test');
   g_form.showFieldMsg('type_of_request','This is a test','info',true);
}
	 else{
 g_form.hideFieldMsg('type_of_request');
 }
}