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

## 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 properties:

- `description`

- `errorName`

- `errorMessage`

The `type` is `error`. The `status` property of the data object contains one of the valid error values listed in Table 13-4.

Table 13-4 Valid Error Values for the Data Object status Property

Values | Description
`emptyResponse` | No Ajax response from server.
`httpError` | One of the valid HTTP errors: `request.status==null` or `request.status==undefined` or `request.status<200` or `request.status>=300`.
`malformedXML` | The Ajax response is not well formed.
`serverError` | The Ajax response contains an `error` element.

In the following example, any errors that occurred in processing the Ajax request are handled by the `handlemyajaxerror` JavaScript function:

    <f:ajax event="click" render="errormessage" onerror="handlemyajaxerror"/>

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