Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Monitoring Events on the Client

To monitor ongoing Ajax requests, use 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: begin, 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 13-3.

Table 13-3 Properties of the onevent Data Object

Property | Description
`responseXML` | The response to the Ajax call in XML format
`responseText` | The response to the Ajax call in text format
`responseCode` | The response to the Ajax call in numeric code
`source` | The source of the current Ajax event: the DOM element
`status` | The status of the current Ajax call: `begin`, `complete`, or `success`
`type` | The type of the Ajax call: `event`

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, `monitormyajaxevent` is a JavaScript function that monitors the Ajax request sent by the event:

    <f:ajax event="click" render="statusmessage" onevent="monitormyajaxevent"/>

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