Search Options in AJAX

<form> 
      <select name="users" onchange="showUser(this.value)"> 
        <option value="">Select a person:</option> 
        <option value="johny">Johny Dawkins</option> 
        <option value="margaret">Margaret Johnson</option> 
        <option value="julie">Julie Doodley</option> 
      </select>
    </form>