Use the following code to create a basic inputEx String Availability.
// Customize you answer : var field2 = new Y.inputEx.SelectField({ label : "Customize the web service response :", name: 'answer', choices: [ { value: 'True' }, { value: 'False' }, { value: 'Error during request'} ], parentEl: 'container2' }); field2.on("updated",function(value) { availabilityField.options.uri = "answer"+field2.getValue(); }); // String availability field var availabilityField = new Y.inputEx.StringAvailability({ parentEl : "container1", // please give a real URI uri : "answerTrue" });