how to detect if try/catch exception handling is supported in browser

[adnanx82@gmail.com]

Hi,

Does anyone know how a script can detect whether exception handling
using try/catch blocks is supported in the browser, so that it can use
them to perform better error handling, and a syntax error is not
produced in cases where they are not supported?

I know that IE and Netscape 5 and above support exception handling (and
older versions don't), but I don't know about other browsers.

Thanks,

-Adnan.

[McKirahan]

Re: how to detect if try/catch exception handling is supported in browser

<adnanx82@gmail .com> wrote in message
news:1116618469 .715466.216690@ g43g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> Does anyone know how a script can detect whether exception handling
> using try/catch blocks is supported in the browser, so that it can use
> them to perform better error handling, and a syntax error is not
> produced in cases where they are not supported?
>
> I know that IE and Netscape 5 and above support exception handling (and
> older versions don't), but I don't know about other browsers.
>
> Thanks,
>
> -Adnan.
>[/color]

Apparently try/catch was added in JavaScript 1.4 (or 1.5) per

http://www.houseoffusion.com/cf_lists/messages.cfm/forumid:4/threadid:40156

JavaScript Version Incompatibiliti es

http://bclary.com/2004/08/27/javascript-version-incompatibilities

has a script to tell you what JS version your browser supports.

Is there an exception/error handling mechanism in core JavaScript?

http://www.faqts.com/knowledge_base/view.phtml/aid/10601

describes what you want (I think).

[Kenneth Tbibetts]

Re: how to detect if try/catch exception handling is supported in browser

If you test the 'typeof' one of the Error classes that is supported in the
version 3 of EcmaScript you can have high confidence that try-catch is also
supported. The return value will be 'function'. A return value of Object
means the null object, and no support. For instance:

if(typeof(windo w.TypeError)==' function'){
go ahead and include try catch code.
}

Warning- I remember Netscape 4 would have conniptions if I even included the
word 'try' in the source code.
Netscape choked on try being a protected keyword even if it never got
called.

I test the client support for document.implem entation and write a script
element in the head, while the page loads.
You can add a filter for try-catch; but so far every client that passes the
document.implem entation test is OK for try catch.

remote script loaded in the document.head as <script type="text/javascript"
src=" test.js"></script>

file test.js:
function loadWch(boo){
var DI= document.implem entation;
if (DI && DI.hasFeature && DI.hasFeature(' html', '1.0')){
var str= (boo)? 'someCodefilepa th': 'otherCodefilep ath';

str='<script type= "text/javascript" + src= "'+ str+ '" > <\/s';
document.writel n(str+'cript>') ;
}
}
loadWch((typeof (window.TypeErr or)=='function' ));

[Kenneth Tbibetts]

Re: how to detect if try/catch exception handling is supported in browser

If you test the 'typeof' one of the Error classes that is supported in the
version 3 of EcmaScript you can have high confidence that try-catch is also
supported.

The return value will be 'function'. A return value of 'object '
means the null object, and no support. For instance:

if(typeof(windo w.TypeError)==' function'){
go ahead and include try catch code.
}

Warning- I remember Netscape 4 would have conniptions if I even included the
word 'try' in the source code.
Netscape choked on try being a protected keyword even if it never got
called.

I test client support for document.implem entation before I include scripts
on a page.

You can add a filter for the Error Type; but so far every client that passes
the
document.implem entation test is OK for try catch.

remote script loaded in the document.head:
<script type="text/javascript" src=" test.js"></script>

file test.js:
function loadWch(boo){
var DI= document.implem entation;
if (DI && DI.hasFeature && DI.hasFeature(' html', '1.0')){
var str= (boo)? 'someCodefilepa th': 'otherCodefilep ath';

str='<script type= "text/javascript" + src= "'+ str+ '" > <\/s';
document.writel n(str+'cript>') ;
}
}
loadWch((typeof (window.TypeErr or)=='function' ));

[adnanx82@gmail.com]

Re: how to detect if try/catch exception handling is supported in browser

Thanks for the replies.

What do you guys think of this solution (below)? To simulate the test
for a browser in which try is not implemented, change the line with
"eval('try {......." to some invalid syntax like "eval('cry {....."
.....

Thanks,

-Adnan.
---------------------
<html>
<script>
var trysupport = 'no';

function on_error(msg, url, line)
{
if (trysupport == 'testing')
{
alert ('try/catch not supported');
}
else
{
alert ('some other error');
}
}
window.onerror = on_error;

function checkTrySupport ()
{
trysupport = 'testing';
eval('try { trysupport = "yes"; } catch (e) {}');
alert('try/catch supported');
}

checkTrySupport ();
</script>
<body>
TRY SUPPORT TEST PAGE
</body>
</html>

[Csaba Gabor]

Re: how to detect if try/catch exception handling is supported in browser

adnanx82@gmail. com wrote:[color=blue]
> Hi,
>
> Does anyone know how a script can detect whether exception handling
> using try/catch blocks is supported in the browser, so that it can[/color]
use[color=blue]
> them to perform better error handling, and a syntax error is not
> produced in cases where they are not supported?[/color]

There was a March 31 thread on this titled:
How to test for try/catch support

http://groups-beta.google.com/group/comp.lang.javascript/browse_frm/thread/dec9b051f64e4b65

Csaba Gabor from Vienna

[Thomas 'PointedEars' Lahn]

Re: how to detect if try/catch exception handling is supported in browser

adnanx82@gmail. com wrote:
[color=blue]
> Does anyone know how a script can detect whether exception handling
> using try/catch blocks is supported in the browser, so that it can
> use them to perform better error handling, and a syntax error is not
> produced in cases where they are not supported?[/color]

This is one of the rare occasions where eval() really comes in handy.
Browsers with script engines that do not support exception handling
(try...catch) have a global `onerror' event handler (specified as part
of the core language instead of the DOM in JavaScript prior to v1.4)
that can be used.

In global context:

var _global = this;


Anywhere "before" the following code is executed:

function dummyError()
{
_global.onerror = null;
return true;
}

In local context:

_global.onerror = dummyError;

eval(new Array(
'try {',
' // do what you want',
'} catch (e) {',
' // handle e',
'}').join("\n") );

dummyError();


PointedEars

[Thomas 'PointedEars' Lahn]

Re: how to detect if try/catch exception handling is supported in browser

adnanx82@gmail. com wrote:
[color=blue]
> What do you guys think of this solution (below)? To simulate the test
> for a browser in which try is not implemented, change the line with
> "eval('try {......." to some invalid syntax like "eval('cry {....."[/color]

It is a nice example and the right approach, however it is invalid HTML[1]
and, more important, will fail compilation in an ECMAScript < 3 script
engine if any try...catch block is included later to accomodate the
detected support; to be seen with Netscape Navigator 4, for example.

I am afraid that it is FWIS not possible to make that feature downwards
compatible in a way that you can execute code that would compile in a
ECMAScript 3+ compliant script engine only if such an engine is present.

However, it is entirely possible to force the ECMAScript 3+ compliant
code via eval() to compile and handle the error when fails to compile.
See my other posting[2] for that.


PointedEars
___________
[1] <http://validator.w3.or g/>
[2] <1342040.NUXyYe 4XEO@PointedEar s.de>