[Javascript] Javascript and FF

[Paul Novitski]

At 8/29/2009 08:17 AM, Del Wegener wrote:
>I have a Javascript calculator
>http://www.edi-cp.com/products_a_series_at_estimator.php
>Which works as intended in IE and I believe it worked in earlier versions of
>FF.  However nothing happens when I use it in FF Version 3.5.2 nor with
>Version 3.0.11


The following might not be relevant to your problems with Firefox 3.5.2, but:

I tried running your script through JSLint, Douglas Crockford's 
JavaScript validator <http://www.jslint.com/>. Turns out JSLint 
doesn't like 'with' statements, so I thought I'd comment them out in 
your script to see if there were any problems beyond them. I didn't 
have time to go through the whole series of warnings & errors for 
your code, but I did notice that your 'with' statements are wonky, e.g.:

   with (Math)
   {
     var k = Math.pow(10,place);
     return (Math.round(numb*k))/k;
   }

This code suggests the existence of Math.Math.pow() and 
Math.Math.round(). The whole idea behind 'with' is that you name the 
object up front and omit it in the block, e.g.:

   with (Math)
   {
     var k = pow(10,place);
     return (round(numb*k))/k;
   }

cf. 
https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Object_Manipulation_Statements#with_Statement

As you probably know, 'with' is not particularly efficient. It has to 
check all of the variables & methods in the block to see if they're 
attached to the object in question. There's no shortcut to doing this 
even with known core objects such as Math: since JavaScript allows us 
to modify objects and their prototypes on the fly, the interpreter 
can't predict which methods and properties an object will or will not 
have from one statement to the next. This suggests that we not use 
'with' in loops that iterate many times. (Your script doesn't do 
this, Del; I'm just talking generally.) It also arguably makes code 
harder to read by us humans without necessarily making the script 
significantly more concise for us nor efficient for the computer. But 
it's certainly a syntactically legal part of the language and in my 
opinion its presence in your script shouldn't trigger validator errors.

The fact that you're mis-using 'with' isn't going to abort your 
script in Firefox (I just tested one of your with blocks and it ran 
fine), it will just eat up a few buckets of machine cycles while 
JavaScript searches the Math object in vain for nonexistent methods. 
Not a big deal. But it is one sign that your code needs cleaning up, 
and that would be one place to start.

JSLint, by the way, is a very strict validator (as Douglas 
emphasizes, "Warning! JSLint will hurt your feelings.") and you need 
to work with it (for example, declare external globals in special 
comments) to get it to approve valid scripting. And it disapproves of 
some bits of scripting style that aren't actual dysfunctional, such 
as using 'with' and calling functions before they're declared in the 
source. But it's a powerful tool that can really help, especially 
with large projects or those niggly little bugs that we can't find 
with our own eyeballs.

Regards,

Paul
__________________________

Paul Novitski
Juniper Webcraft Ltd.
http://juniperwebcraft.com