code: function Prompt() {
    Base.apply(this, arguments);
  
    if (!this.opt.choices) {
      this.throwParamError('choices');
    }
  
    this.opt.validChoices = this.opt.choices.filter(Separator.exclude);
  
    this.selected = 0;
    this.rawDefault = 0;
  
    utils.extend(this.opt, {
      validate: function(index) {
        return this.opt.choices.getChoice(index) != null;
      }.bind(this)
    });
  
    var def = this.opt.default;
    if (utils.isNumber(def) && def >= 0 && def < this.opt.choices.realLength) {
      this.selected = this.rawDefault = def;
    }
  
    // Make sure no default is set (so it won't be printed)
    this.opt.default = null;
  
    this.paginator = new Paginator();
  }
docs: Constructor