| Event handler for |
Image, Window
|
| Implemented in | Navigator 3.0 |
Syntax
onError="handlerText"
Parameters
| JavaScript code or a call to a JavaScript function. |
Description
An error event occurs only when a JavaScript syntax or runtime error occurs, not when a browser error occurs. For example, if you try set window.location.href='notThere.html' and notThere.html does not exist, the resulting error message is a browser error message; therefore, onError would not intercept that message. However, an error event is triggered by a bad URL within an IMG tag or by corrupted image data.
window.onerror applies only to errors that occur in the window containing window.onerror, not in other windows.
onError can be any of the following:
type | Indicates the type of event. |
target | Indicates the object to which the event was originally sent. |
Examples
Example 1: Null event handler. In the following IMG tag, the code onError="null" suppresses error messages if errors occur when the image loads.
<IMG NAME="imageBad1" SRC="corrupt.gif" ALIGN="left" BORDER="2"
Example 2: Null event handler for a window. The
onError="null">onError event handler for windows cannot be expressed in HTML. Therefore, you must spell it all lowercase and set it in a SCRIPT tag. The following code assigns null to the onError handler for the entire window, not just the Image object. This suppresses all JavaScript error messages, including those for the Image object.
<SCRIPT>
However, if the
window.onerror=null
</SCRIPT>
<IMG NAME="imageBad1" SRC="corrupt.gif" ALIGN="left" BORDER="2">Image object has a custom onError event handler, the handler would execute if the image had an error. This is because window.onerror=null suppresses JavaScript error messages, not onError event handlers.
<SCRIPT>
In the following example,
window.onerror=null
function myErrorFunc() {
alert("The image had a nasty error.")
}
</SCRIPT>
<IMG NAME="imageBad1" SRC="corrupt.gif" ALIGN="left" BORDER="2"
onError="myErrorFunc()">window.onerror=null suppresses all error reporting. Without onerror=null, the code would cause a stack overflow error because of infinite recursion.
<SCRIPT>
Example 3: Error handling function. The following example defines a function,
window.onerror = null;
function testErrorFunction() {
testErrorFunction();
}
</SCRIPT>
<BODY onload="testErrorFunction()">
test message
</BODY>myOnError, that intercepts JavaScript errors. The function uses three arrays to store the message, URL, and line number for each error. When the user clicks the Display Error Report button, the displayErrors function opens a window and creates an error report in that window. Note that the function returns true to suppress the standard JavaScript error dialog.
<SCRIPT>
window.onerror = myOnErrormsgArray = new Array()
urlArray = new Array()
lnoArray = new Array()function myOnError(msg, url, lno) {
msgArray[msgArray.length] = msg
urlArray[urlArray.length] = url
lnoArray[lnoArray.length] = lno
return true
}function displayErrors() {
win2=window.open('','window2','scrollbars=yes')
win2.document.writeln('<B>Error Report</B><P>') for (var i=0; i < msgArray.length; i++) {
win2.document.writeln('<B>Error in file:</B> ' + urlArray[i] + '<BR>')
win2.document.writeln('<B>Line number:</B> ' + lnoArray[i] + '<BR>')
win2.document.writeln('<B>Message:</B> ' + msgArray[i] + '<P>')
}
win2.document.close()
}
</SCRIPT><BODY onload="noSuchFunction()">
<FORM>
<BR><INPUT TYPE="button" VALUE="This button has a syntax error"
onClick="alert('unterminated string)"><P><INPUT TYPE="button" VALUE="Display Error Report"
This example produces the following output:
onClick="displayErrors()">
</FORM>Error Report
Error in file: file:///c%7C/temp/onerror.html
Line number: 34
Message: unterminated string literalError in file: file:///c%7C/temp/onerror.html
Line number: 34
Message: missing ) after argument listError in file: file:///c%7C/temp/onerror.html
Example 4: Event handler calls a function. In the following
Line number: 30
Message: noSuchFunction is not definedIMG tag, onError calls the function badImage if errors occur when the image loads.
<SCRIPT>
function badImage(theImage) {
alert('Error: ' + theImage.name + ' did not load properly.')
}
</SCRIPT>
<FORM>
<IMG NAME="imageBad2" SRC="orca.gif" ALIGN="left" BORDER="2"
onError="badImage(this)">
</FORM> See also
onAbort, onLoad
For general information on event handlers, see "General Information about Events".
For information about the event object, see event.
Last Updated: 10/31/97 16:34:02