Events and Event Handlers [Contents] [Previous] [Next] [Index]

onError

Executes JavaScript code when an error event occurs; that is, when the loading of a document or image causes an error.

Event handler for
Image, Window

Implemented in
Navigator 3.0

Syntax

onError="handlerText"

<IMG NAME="imageBad1" SRC="corrupt.gif" ALIGN="left" BORDER="2"
   onError="null">

Example 2: Null event handler for a window. The 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>
window.onerror=null
</SCRIPT>
<IMG NAME="imageBad1" SRC="corrupt.gif" ALIGN="left" BORDER="2">

However, if the 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>
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()">

In the following example, window.onerror=null suppresses all error reporting. Without onerror=null, the code would cause a stack overflow error because of infinite recursion.

<SCRIPT>
window.onerror = null;
function testErrorFunction() {
   testErrorFunction();
}
</SCRIPT>
<BODY onload="testErrorFunction()">
test message
</BODY>

Example 3: Error handling function. The following example defines a function, 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 = myOnError

msgArray = 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"
   onClick="displayErrors()">
</FORM>

This example produces the following output:

Error Report

Error in file: file:///c%7C/temp/onerror.html
Line number: 34
Message: unterminated string literal

Error in file: file:///c%7C/temp/onerror.html
Line number: 34
Message: missing ) after argument list

Error in file: file:///c%7C/temp/onerror.html
Line number: 30
Message: noSuchFunction is not defined

Example 4: Event handler calls a function. In the following IMG 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>

Event handler for	`Image`, `Window`
Implemented in	Navigator 3.0

type	Indicates the type of event.
target	Indicates the object to which the event was originally sent.

onError

Syntax

Parameters

Description

Event properties used

Examples

See also