Force selection of TypeAhead.JS result before form can be submitted.

typeahead-force-selection.js

var checkAutocompleteInput = function() {
  if ($('#autocomplete').find('.tt-selectable').length === 0) { // "#autocomplete" is the autocomplete input menu section
    $('.actions input').attr('disabled', 'disabled') // ".actions input" is the Submit button for the form
  } else {
    $('.actions input').removeAttr('disabled')
  }
};

$('#autocomplete .typeahead').typeahead({...}, {...}).on('typeahead:render', function(e) {
  $('#autocomplete').parent().find('.tt-selectable:first').addClass('tt-cursor');
  checkAutocompleteInput()
});