validateField()
Validate a particular field
validateField(field: String): Promise* presents a required parameter
field* — The field name
fv
.validateField('userName')
.then(function(status) {
// status can be one of the following value
// 'NotValidated' (FormValidation.Status.NotValidated): The field is not yet validated
// 'Valid' (FormValidation.Status.Valid): The field is valid
// 'Invalid' (FormValidation.Status.Invalid): The field is invalid
...
});