It may make sense to use inline validation:
http://www.greghinch.com/yui3-gallery/docs/Form.html#config_inlineValidation
Setting this to true in your form will validate that individual field as soon as it is changed by the user. You can also set "validateInline" to true on individual fields to just do that on specific ones and not the whole form. Finally, you can call "validateField()" on any field at any time to do the validation when it makes sense for you, but you'll have to define when that is specifically for you application.
Hope that helps!
http://www.greghinch.com/yui3-gallery/docs/Form.html#config_inlineValidation
Setting this to true in your form will validate that individual field as soon as it is changed by the user. You can also set "validateInline" to true on individual fields to just do that on specific ones and not the whole form. Finally, you can call "validateField()" on any field at any time to do the validation when it makes sense for you, but you'll have to define when that is specifically for you application.
Hope that helps!