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Question: Can I suppress JavaScript error messages?

Answer: Yes – although usually it is not a good design decision to do so. (Normally, you are much better off fixing the errors, rather than just suppressing the error messages.)

To suppress all JavaScript error messages on your HTML page, you can put the following script code in the <HEAD> section of your page:

<SCRIPT language="JavaScript">
<!--
function silentErrorHandler() {return true;}
window.onerror=silentErrorHandler;
//-->
</SCRIPT>

Or you can use a similar code fragment (without the SCRIPT tags) in an included .js file, if you have one. For a working code example, see this error handling demo!

Question: Can I set up my own JavaScript error handler?

Answer: Yes. To define your own error handler, use this JavaScript code:

function handlerFunction(description,page,line) {
 // put error-handling operators here
 return true;
}
window.onerror=handlerFunction;

Your error handler function can optionally use the following parameters:

a textual description of the error
the address (URL) of the page on which the error occurred
the number of the line in which the error occurred

The error handler function must return false if you wish to invoke the browser's default error handler after your own handler finishes. If you don't want to invoke the browser's default handler, your handler function must return true. For an additional code example, check out this error handling demo!

Question: Can I dynamically change the JavaScript error handler?

Answer: Yes. To change the JavaScript error handler, just setwindow.onerror to the name of the function that will serve as your new error handler.

Here's a demo that lets you test three different error handlers:

the browser's default error handler
an error handler that displays a customized alert box

a "silent" error handler that suppresses all error messages.

Use the select box to set or change the error handler.
Click Fire an Error to test the active error handler.

Below is the source code of the error handling functions used in this demo:

function defaultHandler() {return false}
function silentHandler()  {return true}
function customHandler(desc,page,line,chr)  {
 alert(
  'JavaScript error occurred! \n'
 +'The error was handled by '
 +'a customized error handler.\n'
 +'\nError description: \t'+desc
 +'\nPage address:      \t'+page
 +'\nLine number:       \t'+line
 )
 return true
}