Watch

From PlainOldWebserver

watch()

watch() is a wonderful but forgotten function that monitors variables, alerts you of changes, then allows you to back out of changes if you choose. It also allows a chance to change other variables at the same time.

 var obj = new Object();
 obj.p = 1;
 var c = 2;
 function handle_p(id,old_val,new_val) {
       document.writeln(id+" is now "+new_val);
       return new_val;
 }
 obj.watch("p", handle_p);
 watch("c", handle_p);
 c = 3;
 c = 4;
 obj.p = 2;
 obj.p = 3;

Result:

 c is now 3
 c is now 4
 p is now 2
 p is now 3