 Retrieving additional information about a
JavaScript error through scripting
While you may very well be content with simply using the
onerror event to suppress JavaScript errors, its important to understand
just what happens when the onerror event fires, and use that to create more
complicated onerror functions.
Whenever the onerror event fires, JavaScript logs all
information regarding the error and provides you with a mean to access it.
The info I'm referring to is the same info shown inside the default browser
error dialog whenever a js error occurs. First off, lets examine what the
default error box of your browser tells you in the event of an error. The
information inside usually looks something like this:
JavaScript Error:
http://javascriptkit.com/test.htm, line 8:
missing ) after argument list.
document.write('hi there'
..........................^
The default error box always informs the surfer the url of
the page containing the error, the line where the error occurred, and a
(less than helpful, I might add) message attempting to explain why the error
occurred. Using JavaScript, we have access to the same information provided
by the default box, realized through optional parameters you can specify
inside the function to be executed when the onerror event fires. (Don't
worry, all this will become clear very soon):
|
Parameter |
function |
| 1st parameter |
Contains the message explaining why the error occurred. |
| 2nd parameter |
Contains the url of the page with the error script |
| 3rd parameter |
Contains the line number where the error occurred |
Lets clear the mist and modify our original error code of
the previous page so that it alerts us information regarding the error:
<head>
<script type="text/javascript">
function tellerror(msg, url, linenumber){
alert('Error message= '+msg+'\nURL= '+url+'\nLine Number= '+linenumber)
return true
}
window.onerror=tellerror
</script>
<script>
document.write('hi there'
</script>
</head>
Click here to
see an actual demo.
The key to the above are the three parameters inside
function tellerror(). When defined, JavaScript uses them to store the error
information. The parameters can be any name.
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