javascript - Open selectbox option using jquery -

i want show selectbox option using jquery when page loads. have used .simulate() , .trigger function it's not working, can please suggest solution that.

code:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script> <script src="simulate.js"></script> <script> $(document).ready(function(){     $("#test").simulate('mousedown'); // not working     $("#test").trigger('click'); // not working     //$("#test").attr('size',3); // size not need. want display option dropdown shows. }); </script>  <select id="test">    <option value="0">select option</option>    <option value="1">1</option>    <option value="2">2</option>    <option value="3">3</option> </select> 

please me out problem...

try this...

$(document).ready(function(){      var mydropdown=$("#test");     var length = $('#test> option').length;     mydropdown.attr('size',length);     $("#test").click(function(){         mydropdown.attr('size',0);     });   });