JavaScript » eventhandler » onError
- Syntax:
- onError = myJavaScriptCode
Event handler for Image, Window.
The onError event handler executes the specified JavaScript code
or function on the occurance of an error event. This is when an image
or document causes an error during loading. The distinction must be made
between a browser error, when the user types in a non-existant URL, for
example, and a JavaScript runtime or syntax error. This event handler
will only be triggered by a JavaScript error, not a browser error.
As well as the onError handler triggering a JavaScript function,
it can also be set to onError="null" which suppresses the standard
JavaScript error dialog boxes. To suppress JavaScript error dialogs when
calling a function using onError, the function must return true
(example 2 below demonstrates this).
There are two things to bear in mind when using window.onerror.
Firstly, this only applies to the window containing window.onerror, not
any others, and secondly, window.onerror must be spelt all lower-case
and contained within <script> tags; it cannot be
defined in HTML (this obviously doesn't apply when using onError
with an image tag, as in example 1 below).
The onError event handler uses the following Event
object properties.
type - this property indicates the type of event.
target - this property indicates the object to which the event
was originally sent.
Examples
Code:
<IMG NAME="imgFaulty" SRC="dodgy.jpg onError="null">Explanation:
This suppresses the normal JavaScript error dialogs if a problem arises when trying to load the specified image.
Code:
<script type="text/javascript" language="JavaScript">
s1 = new String(myForm.myText.value)
window.onerror=myErrorHandler
function myErrorHandler() {
alert('A customized error message')
return true
}
</script>
<body onload=nonexistantFunc()>Explanation:
This example does the same as the previous one, but applied to a window, by using return true in the called function, and displays a customized message instead.
See Also:
