If I understand, when the typeahead component loses the focus, the user should be alerted that its input is invalid if it is not in the list?

The code will thus be something like this :

var myData = [...]; // This array will contain all your possible data for the typeahead



$(#my-type-ahead).typeahead({source : myData})

                   .blur(validateSelection);



function validateSelection() {

    if(source.indexOf($(this).val()) === -1) 

        alert('Error : element not in list!');

}

Just be careful about the fact that indexOf is not implemented in IE6-8. But shims can be found, for example : Best way to find if an item is in a JavaScript array? .