onerror Property
Returns or sets a Variant that represents the value of the onerror attribute that is the name of the script to run when the onerror event fires.
expression.onerror
expression Required. An expression that returns one of the objects in the Applies To list.
Example
The following example sets the onerror attribute for the first IMG element in the active document.
Dim objImage As FPHTMLImg
Set objImage = ActiveDocument.images.Item(0)
objImage.OnError = "script()"