Here is the simple Javascript code to open select box with a button click.
This javascript code also works for toggling the select box.
<script type="text/javascript"> function expandSelect(id){ var select_flag = document.getElementById('select_flag').value; if(select_flag==1){ var select_box = document.getElementById(id); select_box.size = 1; document.getElementById('select_flag').value = 0; }else{ var select_box = document.getElementById(id); select_box.size = select_box.options.length; document.getElementById('select_flag').value = 1; } } </script> <button onclick="expandSelect('select_box')"> Toggle Select Box </button> <div id="container"> <select name="select_box" id="select_box" > <option value="">Select</option> <option value="">option1</option> <option value="">option2</option> <option value="">option3</option> <option value="">option4</option> <option value="">option5</option> <option value="">option6</option> </select> <input type="hidden" name="select_flag" id="select_flag" value="0"> </div>