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The throw statement provides a way to create an exception which will be passed to an associated catch() handler in a try ... catch structure. It is really intended to be used in that context, but you can use it outside of a try ... catch structure and trap the exception with the normal onError event handling support.
You can use this mechanism to generate an error, perhaps as a result of testing some value. Placing a throw statement into your code will force the error handling to be invoked. However if you use it outside of a try ... catch block, the browser error handling will generate an error due to there being no way of catching the thrown event. It forces an error dialog, but not the one you wanted. You need to use a throw with a try ... catch block to force the catch code to be called.
You can work around this by assigning an error handler function to the onerror property and making sure that the error handler returns a Boolean true value to signify that the error has no further processing required.
This is not supported by Netscape Enterprise Server 3, and so its error handling capabilities are not available server-side.
When using MSIE version 5 on the Macintosh platform, if you set the LANGUAGE HTML tag attribute of the enclosing <SCRIPT> tag to JScript 1.3, this handler will not be invoked properly.
The example below, while supported on Netscape 6.0, does not seem to be supported on Internet Explorer 5.0 or 5.5.
<HTML>
<HEAD>
</HEAD>
<BODY>
<SCRIPT>
// Define an error handler function
function myErrHandler(anException)
{
alert("An error happened and was caught by this handler.");
return true;
}
// Register the error handler
onerror = myErrHandler;
// Throw an exception
throw "ERR";
</SCRIPT>
</BODY>
</HTML>ECMA 262 edition 2 - section - 7.4.3
ECMA 262 edition 3 - section - 7.5.2
ECMA 262 edition 3 - section - 12.13
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JavaScript Programmer's Reference, Cliff Wootton Wrox Press (www.wrox.com) Join the Wrox JavaScript forum at p2p.wrox.com Please report problems to support@wrox.com © 2001 Wrox Press. All Rights Reserved. Terms and conditions. | ||