Topic awaiting preservation: Avoiding errors

In some part of the body of my html code, I have:

<script language="JavaScript" type="text/javascript">Wpic();</script>

Wpic() is a function that writes part of the code to show a picture.

On the header, I have:

<script language="JavaScript" type="text/JavaScript" src="popup.js"></script>

Let's suppose the visitor save the html page locally without saving the corresponding popup.js file. When he tries to open the html page, he'll get an error, since there is no popup.js available.

Is there a way to avoid this error? (in other words, is there a way to open the .html file without having the related .js file, and NOT getting an error?)

Thanks.

window.onerror = function() { return false; }

if you put that line in your script and the viewer won't get any message when there is an error in your script.

-= Veneficuz =-
"Mundus vult decipi. Ergo decipiatur."

The code provided doesn't work if IE 6 is configured to "Display a notification about every script error" and to not "Disable script debugging".
Is it supposed to be this way?
Thanks.

Actually, error handler function should return true instead of false. The correct code is:

window.onerror = function() { return true; }

Max's code will work fine.

Rule of thumb though, I don't code for browsers that use something outside the default settings. (as in your example).

personally if the file is not getting included you should find out why instead of repressing the errors.



.:[ The Tao of Steve ]:.
Be Desireless
Be Excellent
Be Gone
...................................

Huh! Would ya look at that.

Just what I was looking for. Works like a charm too!

Espically usefull when your triggering functions in one window that act on another window with setTimeouts. Trying to avoid errors if you closed one window when those timeouts are still running was starting to wear on me.

Yes, Max's code worked fine.
I like my pages without visible errors. While making them, I disable the line, so I'm aware of any error, then, when I'm going to post it, I enable the line.
Thanks!

The easiest way to avoid an error like that is to check for the function's existence first:

<script language="JavaScript" type="text/javascript">if (Wpic) Wpic();</script>

That actually will error.

Testing for something that has not been defined will error in JS (works in some languages though)



.:[ The Tao of Steve ]:.
Be Desireless
Be Excellent
Be Gone
...................................

No. Testing for something that hasn't been defined in JS will return false.

The problem occurs when you treat something that hasn't been defined as an object, and check if one of its properties is defined; for example:

if (thisVariableDoesntExist) doSomething();
// works fine, it will *not* call the doSomething function.

if (thisVariableDoesntExist.inexistantProperty) doSomething();
// causes an error. can't access the property of an inexistant object.

This is why stuff like "if(document.layers) NN = true;" works.

hlaford's code results in error, in IE6. I didn't test it for other browsers.
I like the idea of a global and easy way to turn on and off the error checking (Max's code).

I'm willing to bet that hlaford's code fails because even though the Wpic function exists, it's something inside of it that's causing the error.

In any case, if Max's code works, go ahead and use it. I for one very rarely use that code; it seems like a slightly irresponsible way of avoiding errors... I find places where errors might appear and then test against the problems. That way, I have control over what happens when there's a problem - otherwise, a piece of code might run halfway, and cause an error, and just stop abruptly, leaving something unfinished and looking strange to the user.

if you didn't like the first iteration, try checking typeof:

if (typeof Wpic == "function") Wpic();

typeof will return "undefined" if Wpic has not been declared.

Wpic just opens a window and write to an htm file.

==========================

Contents of popup.js:

function Wpic(Pindex) {
if (window.document.bgColor == "#99ccff") Cor=1; else Cor=2;
avHTM = '<a href="JavaScript:void(0);" onclick="return popItUp(' + eval(Pindex) + ',' + Cor + ');" target="popJWin">';
avHTM += '<img border="1" src="thumbs/_' + eval("F" + Pindex) + '" align="right" hspace="5" vspace="3" width="180" height="135" Alt="Click me"></a>';
document.write(avHTM); }

function popItUp(pIndex,Kor) {
popUpWin = window.open('screenshot.htm?img=shots/'+eval("F" + pIndex)+'&caption='+eval("L" + pIndex)+'&cor='+Kor,
'popJWin','resizable=yes,scrollbars=no,menubar=no,width=535,height=420,left=5,screenX=5,top=5,screenY=5'); // pic is 500 x 375
popUpWin.resizeTo(535+12,420+38)
popUpWin.focus();
return false; }

==========================

Contents of screenshot.htm:

<html>
<head>
<title>Screenshot - MOHAA</title>
<style type="text/css">
<!--
TD {text-decoration:none;font-family:trebuchet ms;font-size:8pt;}
// -->
</style>
<script language="JavaScript" type="text/JavaScript" src="script/sshot.js"></script>
</head>
<script type="text/javascript">insertBody();</script>
<div align="center">
<center>
<table border="3" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="500">
<tr>
<td width="100%"><script type="text/javascript">insertImg();</script></td>
</tr>
</table>
</center>
<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="500">
<tr>
<script type="text/javascript">insertTDTag();</script>
<script type="text/javascript">insertCaption();</script></td>
</tr>
</table>
</div>
</body>
</html>

==========================

Contents of sshots.js (not originally written by me, just modified by me - used with permission):

/**
* Get data from a query string into a hash object
* @param encoded_data A url encoded string (like ?a=abc&b=xyz)
* @return a hash object of property/value pairs
*/
function extractQueryData(encoded_data)
{
var query_data = new Object;
var query_start = encoded_data.indexOf('?');
if(query_start != -1)
encoded_data = encoded_data.substr(query_start+1);
var data_array = encoded_data.split('&');
var i;
for(i=0; i < data_array.length; i++)
{
var data = data_array[i].split('=');
var prop = data[0];
var val = unescape(data[1]);
query_data[prop] = val;
}
return query_data;
}

var Query = extractQueryData(location.search);

/// Write out the image tag
function insertImg()
{
var imgsrc = Query["img"];
document.write('<img border="0" src="' + imgsrc + '" width="500" height="375">');
}

/// Write out the image caption
function insertCaption()
{
var caption = Query["caption"];
document.write(caption);
}

/// Write out the backgound tag/color
function insertBody()
{
var colori = Query["cor"];
if (colori == 1)
document.write('<body bgcolor="#B7DBFF">'); else
document.write('<body bgcolor="#d1dd99">');
}

/// Write out the TD font color tag
function insertTDTag()
{
var colori = Query["cor"];
if (colori == 1)
document.write('<td width="100%" style="color:#000080;">'); else
document.write('<td width="100%" style="color:#006000;">');
}


==========================

Contents of a sample html page that uses Wpic() - here is where the onerror function is located:

<html>
<head>
<title>Title goes here...</title>
<script language="JavaScript" type="text/JavaScript" src="script/popup.js"></script>
<script language="JavaScript" type="text/javascript">
<!--
window.onerror = function() { return true; }
var F1='name_of_a_file_1.jpg';
var L1='Pic. 1 - Legend 1';
var F2='name_of_a_file_2.jpg';
var L2='Pic. 2 - Legend 2.';
// -->
</script>
<link rel="stylesheet" type="text/css" href="script/green.css">
</head>
<body>
<p> blabla... </p>
<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="100%">
<tr><td width="100%" class="txt">
<script language="JavaScript" type="text/javascript">Wpic(1);</script>
<b>1.</b>&nbsp; Bla bla bla ... (pic. 1).</td></tr>
<tr><td width="100%">&nbsp;</td></tr>
<tr><td width="100%" class="txt">
<script language="JavaScript" type="text/javascript">Wpic(2);</script>
<b>2.</b>&nbsp; Bla bla bla ... (pic. 2)</td></tr>
</table>
<p> blabla... </p>
</body>
</html>

Here is a live sample of all the code above working: http://www.viol.net/mohaa/tips_resistance.htm

Serious Slime you can try that code as is it error in a normal setup IE browser. I've run into that a lot with popup trying to test for windows that are open that I've named. something like:

function openwin() {
myWin = window.open(..... etc.

}

if (myWin) myWin.location.href = url;
else openwin(url);


That has always fails if you try to run the if without having run the function first. Works fine though if you set mywin false early in the script.

I think it has to do with the lack of typecasting and variable definitions (the "$") in JS.



.:[ The Tao of Steve ]:.
Be Desireless
Be Excellent
Be Gone
...................................

You know what? you're right. How strange. I just tried it on my own page and it failed. However, this *did* work:

if (window.Wpic) Wpic();

I'm not sure why.

lol

That is funny. Silly programming languages



.:[ The Tao of Steve ]:.
Be Desireless
Be Excellent
Be Gone
...................................

Whay not to use the try catch (IE5+,Netscape6) to avoid errors?
It can be very useful to group code with one error handling.

try{
var a = docu.....

} catch(e){
alert("....");
}