Client-side validation of text fields
The CSValidator component extension allows client-side validation of TextField, PasswordField, and TextArea components. The field value is validated after each key press without any client-server communication.
The add-on is installed as a JAR, which includes the JavaDoc for the server-side API. You need to compile the widget set.
The version 0.5 and later support Vaadin 7, and come as a component extension, which you can attach to a text field with extend(). For Vaadin 6 compatibility, use version 0.4.x, which offers three components instead of an extension: CSValidatedTextField, CSValidatedPasswordField, and CSValidatedTextArea. The functionality is exactly the same.
The add-on should be considered as beta, as compatibility is not tested with IE, but it probably works.