Set global variable from within a Class

Bruce · Oct 2, 2008

From within a class instantiation, I'm trying to set the value of a
global variable. Let's call that variable "x". I know I can do this

window.x = 5;

and it will work but I really need to do this:

x = 5;

The above works in Firefox 2 but not in IE6. Actually, I'm trying to
do this

eval("x = 5");

For reasons that are too long to explain, I can't do this

eval("window.x = 5");

(which I realize would also work) because I can't alter the variable
name. It has to be "x"

Any thoughts on how I can do this within the scope of a Class? I know
this is non standard and might seem odd or inadvisable but it's a long
story that will be solved if someone can help with my problem.

Bruce · Oct 2, 2008

Never mind. The cause of my problem is something completely different.
See the thread "id names are global variables?"

Jeremy J Starcher · Oct 2, 2008

On Thu, 02 Oct 2008 11:19:26 -0700, Bruce wrote:

Are you *sure* this is a good idea?

eval("x = 5");

Eval is very seldom the correct tool to use.

For reasons that are too long to explain, I can't do this

eval("window.x = 5");

If you *must* use eval, why can you not:
{ eval("x = 5"); window.x = x; }

Any thoughts on how I can do this within the scope of a Class? I know
this is non standard and might seem odd or inadvisable but it's a long
story that will be solved if someone can help with my problem.

Tested in Fx 3.0.2, IE6 and Opera (something)

<html>
<head>
<title>Test</title>
</head>
<body>

<script type="text/javascript">

function w(s)
{
document.write(s + "<br>");
}

var _global = (function() {return this})();
var x = 10;

(function() {
var x = 5;
w("Anon function start");
w("Inner: x= " + x);
w("_global.x= " + _global.x);

w("Showing we don't get a primitive reference");
x = _global.x; // This makes a COPY of _global.x
x = 8; // And this line doesn't affect global x at all
w("Inner: x= " + x);
w("_global.x= " + _global.x);

w("Anon function inside an anon function finds the 'closest' x");
(function() { // Even in a new scope, it will find "inner_x" first.
x = 18;
})();
w("Inner: x= " + x);
w("_global.x= " + _global.x);

w("As does eval");
eval("x = 22");
w("Inner: x= " + x);
w("_global.x= " + _global.x);

// Note: I CANNOT actually recommend that someone USE this method.
// The use of "with" is considered evil by many for very good reason.
// If this is the "solution" to a problem, I'm willing to wager you
have
// have far bigger problems.
//
// "with" is considered bad form by many. Don't do it.
w("But the WITH statement is ... magic");
with(_global) {
x = 15;
}
w("Inner: x= " + x);
w("_global.x= " + _global.x);

w("But the WITH statement is ... magic -- with eval");
with(_global) {
eval("x = 25");
}
w("Inner: x= " + x);
w("_global.x= " + _global.x);

})();

w("And the end, we have: global x= " + x);

</script>

</body>
</html>

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Set global variable from within a Class

Bruce

Bruce

Jeremy J Starcher

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