Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

JavaScript 1.1; buggy in Netscape 6/6.1

Synopsis

You register an onerror event handler like this:

window.onerror=handler-func

The browser invokes the handler like this:

window.onerror(message, url, line)

Arguments

message

A string that specifies the error message for the error that occurred.

url

A string that specifies the URL of the document in which the error
occurred.

line

A number that specifies the line number at which the error occurred.

Returns

true if the handler has handled the error and
JavaScript should take no further action; false if
JavaScript should post the default error message dialog box for this
error.

Description

The onerror property of the Window object
specifies an error handler function that is invoked when a JavaScript
error occurs in code executing in that window. By default, JavaScript
displays an error dialog box when an error occurs. You can customize
error handling by providing your own onerror event
handler.

You define an onerror event handler for a window
by setting the onerror property of a Window object
to an appropriate function. Note that unlike other event handlers in
JavaScript, the onerror handler cannot be defined
in an HTML tag.

When the onerror handler is invoked, it is passed
three arguments: a string specifying the error message, a string
specifying the URL of the document in which the error occurred, and a
number that specifies the line number at which the error occurred. An
error handling function may do anything it wants with these
arguments: it may display its own error dialog box or log the error
in some way, for example. When the error handling function is done,
it should return true if it has completely handled
the error and wants JavaScript to take no further action or
false if it has merely noted or logged the error
in some fashion and still wants JavaScript to display the error
message in its default dialog box.

Note that while this event handler returns true to
tell the browser to take no further action, most Form and form
element event handlers return false to prevent the
browser from performing some action, such as submitting a form. This
inconsistency can be confusing.

You can turn off error handling entirely for a window by setting the
onerror property of the window to a function that
returns true and does nothing else. You can
restore the default error-handling behavior (the dialog box) by
setting onerror to a function that returns
false and does nothing else.

Bugs

This event handler is correctly triggered by errors in Netscape 6 and
Netscape 6.1, but the values passed as the message, URL, and line
number arguments are incorrect, so although you can use it to detect
the occurrence of an error, you cannot use it to obtain any useful
information about the error.