Use asynchronous validator if the validation can not be computed immediately, but is provided through a callback. The widget automatically shows a spinning indicator while the validity of the widget is computed. This validator caches the result.
<input type="text" ng:validate="asynchronous:validate[:update]"/>
angular.validator.asynchronous(value, validate[, update])
value – {string} –
value to validate
validate – {function(inputToValidate,validationDone)} –
function to call to validate the state of the input.
update(optional=noop) – {function(data)} –
function to call when state of the validator changes