Using Ajax with JavaServer Faces Technology - The Java EE 6 Tutorial: Advanced Topics - page 75

Monitoring Events on the Client
The ongoing Ajax requests can be monitored by using the onevent attribute of the
f:ajax tag. The value of this attribute is the name of a JavaScript function. JavaServer
Faces calls the onevent function at each stage of the processing of an Ajax request: be-
gin, complete, and success.
When calling the JavaScript function assigned to the onevent property, JavaServer
Faces passes a data object to it. The data object contains the properties listed in Table 4-3 .
TABLE 4-3. Properties of the onEvent Data Object
By using the status property of the data object, you can identify the current status
of the Ajax request and monitor its progress. In the following example, mon-
itormyajaxevent is a JavaScript function that monitors the Ajax request sent by the
event:
<f:ajax event="click" render="errormessage"
onevent="monitormyajaxevent"/>
Handling Errors
JavaServer Faces handles Ajax errors through use of the onerror attribute of the
f:ajax tag. The value of this attribute is the name of a JavaScript function.
When there is an error in processing a Ajax request, JavaServer Faces calls the defined
onerror JavaScript function and passes a data object to it. The data object contains all
the properties available for the onevent attribute, and in addition, the following proper-
ties:
• description