如何在条件存在时选择特定选项

Question

I want to select the specific option in drop down list when a condition is existed.I set the Session in php and if the combo box has the value of 1 , it will be shown the option with value 1. I mean if session is 1, select the option with value of 1, if session is 2, select the option with vlaue of 2, and so on... . I want to set automatically select(I see the changes) with session in php. sth like blewo:

<select id="sel" >
  <option value='1'>one</option>
  <option value='2'>two</option>
  <option value='3'>three</option>
</select>
 <?php $_SESSION['num']='1'; ?>
<script>
  //must be shown the option with value of `1`.
<script>

Answer 1

Try this .

<select id="sel" >
  <option value='1'>one</option>
  <option value='2'>two</option>
  <option value='3'>three</option>
</select>
 <?php $_SESSION['num']='1'; ?>
<script>

    //set local variable value so that I don't have to do it for each of the following ways to do this.
    var num =  "<?php echo $_SESSION['num']; ?>";

    //normal javascript 
    document.getElementById("sel").value = num;

    //using jQuery  
    $("#sel").val(num);

<script>

Or this try vikingmaster's way