Class TextInput

var action = CardService.newAction()
    .setFunctionName('suggestionCallback')
    .setParameters({'numSuggestions': 3});

CardService.newTextInput()
    .setFieldName('option-field')
    .setTitle('Option Selected')
    .setSuggestionsAction(action);

// ...

function suggestionCallback(e) {
  var suggestions = CardService.newSuggestions();
  var numSuggestions = parseInt(e.parameter['numSuggestions']);
  for(var i = 1; i <= numSuggestions; i++) {
    suggestions.addSuggestion('Suggestion ' + i);
  }
  return CardService.newSuggestionsResponseBuilder()
      .setSuggestions(suggestions)
      .build();
}