How does firebug watch global variables

[Yel]

When debugging javascript with firebug, all global variables can be
watched in the "watch" window.
The thing I'm wondering is how does firebug list these variables.
I get the sources of firebug but cannot find where firebug does it.

[John J Barton]

I guess I don't understand. Just use for-in loop over "window"
properties?
You must have something else in mind.
jjb

[Yel]

On Oct 30, 12:44 pm, John J Barton <johnjbar...@johnjbarton.com>
wrote:

> I guess I don't understand. Just use for-in loop over "window"
> properties?
> You must have something else in mind.
> jjb

Yeah, for-in loop over "window" does work in Firefox, although I
cannot make sure
if firebug really works in this way.
BTW: for-in loop cannot list global variables in IE6/7/8 except they
are declared like
"window.gVar = xxx". I guess that's why IE Developer Toolbar cannot
tell global
variables or debug it.

[Maciej Jaros]

Hmm... That's interesting. In all browsers below code will give you
alert with 123:
javascript:var xxx = 123;alert(window.xxx)

But output of below function is browser's engine dependant:
var xxx = 123
function test()
{
var out = document.getElementsByTagName('textarea')[0]
for (var obj in window)
{
if (typeof(window[obj])!='function')
out.value+='\nwindow.'+obj +' => ('+typeof(window[obj])+')
'+ window[obj];
}
}

In FF it will show you quite a lot of stuff and your global variables.
In Chrome you will get even more as some "null" variables will be shown
(like window.on*).
In IE you will get pretty much the same as in Chrome, but without global
variables.
And in Opera... Well I was kinda shocked, because the output was
"window.opera => (object) [object Opera]" :-)). Then I noticed some of
stuff linked to window object in Opera doesn't have toString methods so
you'll have use something like:
{out.value+='\nwindow.'+obj +' => ('+typeof(window[obj])+') '+
window[obj];}catch (e){}
And then it will work in Opera too and it will show you global vars.

And as you said before setting window.xxx rather then var xxx will make
it work for IE too. Still watching the variable xxx in IE's dev tool
_is_ possible in both situations. The only drawback is that you won't
see your watch if you're not debugging (simply switching to debugging
won't work - you'll have to break on some point).

Regards,
Nux.

[John J Barton]

On Oct 29, 10:53 pm, Yel <richardr...@gmail.com> wrote:
> On Oct 30, 12:44 pm, John J Barton <johnjbar...@johnjbarton.com>
> wrote:
>
> > I guess I don't understand. Just use for-in loop over "window"
> > properties?
> > You must have something else in mind.
> > jjb
>
> Yeah, for-in loop over "window" does work in Firefox, although I
> cannot make sure
> if firebug really works in this way.

Firebug's dom.js (the code that supports the Watch side panel) applies
getMembers() to what ever object is the current selection for the
panel. The default selection is this.context.getGlobalScope() and
tabContext.js shows us that the global scope for a context in Firebug
is "this.window", another words the window object for the current
Firebug context. (Chromebug supports non-window scopes).

And getMembers uses for-in loop to get the properties of its current
selected object.
jjb

[Yel]

continue with this topic.

I wrote some scripts to try to loop all objects in the browser (say,
firefox), and made it below :

{{{
<script type="text/javascript">

function Hashtable()
{
this._hash = new Object();
this.add = function(key,value){
if(typeof(key)!= "undefined"){
if(this.contains(key)==false){
this._hash[key] = (typeof(value)=="undefined"?
null:value);
return true;
} else {
return false;
}
} else {
return false;
}
}
this.remove = function(key){delete this._hash[key];}
this.count = function(){var i=0;for(var k in this._hash){i++;}
return i;}
this.items = function(key){return this._hash[key];}
this.contains = function(key){return typeof(this._hash[key])!=
"undefined";}
this.clear = function(){for(var k in this._hash){delete this._hash
[k];}}
this.toString = function(){
var str = [];
for (var i in this._hash){ str.push(i.toString()); }
return str.join("<br />");
}
}

var vars = new Hashtable();
function takesnapshot()
{
list = function(obj)
{
if(obj.toString() == 'vars') return; // exclude vars self.
vars.add(obj.toString(), obj.toString());
for(var p in obj) list(p);
}
list(window);
// now, vars is a snapshot of window.
}

setTimeout(takesnapshot, 10);
setTimeout(function(){
alert("vars len = " + vars.count());
document.body.innerHTML = vars.toString();
}, 2000);

</script>
}}}

However, it didn't output what I wanted. Moreover, the output differed
between IE and firefox (or Chrome etc.)
Is it caused by the single threading implementations of javascript?
Thanks for any idea.

[John J Barton]

On Nov 23, 6:25 pm, Yel <richardr...@gmail.com> wrote:
> continue with this topic.
>
> I wrote some scripts to try to loop all objects in the browser (say,
> firefox), and made it below :
>
> {{{
> <script type="text/javascript">
>
> function Hashtable()

...

> var vars = new Hashtable();

Just a suggestion, read up some on Javascript, say for example, Doug
Crockford's book "Javascript the Good Parts". That code looks like
Java...

> function takesnapshot()
> {
>     list = function(obj)
>     {
>         if(obj.toString() == 'vars') return; // exclude vars self.
>         vars.add(obj.toString(), obj.toString());

? I guess you meant to add p, obj[p].toString()?

>         for(var p in obj) list(p);

You are passing the field name in to list.

>     }
...

> However, it didn't output what I wanted. Moreover, the output differed
> between IE and firefox (or Chrome etc.)

Sure it will be different. Some the same some different.

> Is it caused by the single threading implementations of javascript?

Huh? No.
jjb