How to prevent typeahead from filling in the input with the selected value?

I am using bootstrap-typeahead and rails4.

I can get the dropdown feature but when I press up and down, I don't want the selected value to fill in the input. How can I implement this?

I tried some solutions but they didn't work. How to prevent Twitter typeahead from filling in the input with the selected value?

Relevant code:

$("#nav_search").typeahead({
  items: 6,
  source:numbers.ttAdapter(),
  displayText: function(data){
      // console.log(data);
      return '<div><strong>'+data.username+'</strong>'+'-'+data.position+' at '+data.company+'</div>';
  },
  fitToElement: true,
  afterSelect: function(data){
    window.location.href=data.url;
  }
})