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Error Reporting

</script>

</head>

</body>

</html>

When this page loads, the

handleLoad()

function is called and an exception occurs when trying to call

a non-existent method of the window object. That thread is then exited so the

alert(“Loaded”);

line is

never executed. When the user clicks on the button, however, the

handleClick()

function is still called

and an alert displays the text

“Clicked.”

Error Reporting

Because each browser has its own built-in JavaScript interpreter (including its own mechanisms for

tracking down errors while interpreting), each reports errors in different ways: Some pop up an error

message; others simply log the message to a JavaScript console. Regardless of the method used, be

aware of where this data is located on your target browsers. Browsers such as Internet Explorer, Mozilla,

Safari, and Opera each have their own unique ways of presenting this data. This section guides you to

the error message information for each of them.

Internet Explorer (Windows)

Microsoft’s flagship browser, Internet Explorer for Windows, is capable of reporting errors in a couple of

different ways. By default, Internet Explorer pops up a dialog with the error details (Figure 14-1) and

asks if you want to continue running scripts on the page. This is misleading, because clicking either Yes

or No allows other scripts to continue running.

Figure 14-1

If the browser has a debugger (such as Microsoft Script Debugger, which is discussed later in this chap-

ter), the dialog offers the option to debug the script or ignore it (Figure 14-2). Clicking Yes on this dialog

brings you into the debugger; clicking No simply closes the dialog.

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Error Handling

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