Subj : Getting string objects to compare equal
To   : netscape.public.mozilla.jseng
From : Steve Evans
Date : Tue Sep 20 2005 03:59 pm

Here's a snippet of alas-all-too-common script from a website:

if (theForm.frmEmail.value != theForm.frmEmailConf.value) {
	errAlert("The E-mail addresses entered do not match")
	return false
}

This is comparing two string *objects*, which is like 
comparing two C strings using == instead of strcmp(). It 
should always fail. One of the string objects should have 
been stringified with toString() to force the JS engine to 
do a string comparison.

And yet it works in current versions of Firefox and Opera 
and IE, but not in my embedded SpiderMonkey environment, 
which fails "correctly", as per the JS spec.

For a while I thought that maybe Firefox interned the values 
of the form controls using JS_InternString(), so that the 
frmEmailConf.value really does use the same JSString as 
frmEmail.value.  However, a grep through the source reveals 
that JS_InternString() is only used for read-only constant 
strings that will really benefit from re-use: attribute 
names rather than attribute values.

So how do I emulate Firefox's forgiving behaviour?

.