Entry
How can I detect when a variable change value
Aug 24th, 2001 16:05
Juergen Thelen, Dario Copia,
Hi Dario,
With NN4 and NN6 you can use the watch() and unwatch() methods, that
are inherited by every object (that was descended from an Object).
Here's a sample showing this technique:
--- snip ---
<HTML>
<HEAD>
<TITLE>Untitled Document</TITLE>
<META http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<SCRIPT language="JavaScript1.2">
<!--
var myGlobal = "hello";
window.watch("myGlobal", function (id, oldValue, newValue)
{
document.writeln("window." + id + " was " + oldValue +", now: " +
newValue + '<BR>');
return newValue;
});
myGlobal = "world";
myObject = new Object();
myObject.myProperty = 4711;
myObject.watch("myProperty", function (id, oldValue, newValue)
{
document.writeln("myObject." + id + " was " + oldValue +", now: " +
newValue);
return newValue;
});
myObject.myProperty = 9876;
//-->
</SCRIPT>
</HEAD>
<BODY bgcolor="#FFFFFF" text="#000000">
</BODY>
</HTML>
--- snap ---
IE and most other browsers unfortunately do not implement the watch()
and unwatch() methods, so I usually simply write the values of the
variables I am interested in into either an alert box (using alert()),
or into the windows statusbar (using window.status = variable).
For IE5 you can also use the onpropertychange event, which is similiar
to watch(), but afaik this works only for its DOM properties. Never
tested it...
Hth, Juergen
