make select option selected javascript

1document.getElementById('personlist').getElementsByTagName('option')[11].selected = 'selected'
2

1<form name="AddAndEdit">
2   <select name="list" id="personlist">
3      <option value="P1">Person1</option>
4      <option value="P2">Person2</option>
5      <option value="P3">Person3</option>
6   </select>
7</form>

1(function() {
2    
3    // get references to select list and display text box
4    var sel = document.getElementById('scripts');
5    var el = document.getElementById('display');
6
7
8    function getSelectedOption(sel) {
9        var opt;
10        for ( var i = 0, len = sel.options.length; i < len; i++ ) {
11            opt = sel.options[i];
12            if ( opt.selected === true ) {
13                break;
14            }
15        }
16        return opt;
17    }
18
19    // assign onclick handlers to the buttons
20    document.getElementById('showVal').onclick = function () {
21        el.value = sel.value;    
22    }
23    
24    document.getElementById('showTxt').onclick = function () {
25        // access text property of selected option
26        el.value = sel.options[sel.selectedIndex].text;
27    }
28
29    document.getElementById('doLoop').onclick = function () {
30        var opt = getSelectedOption(sel);
31        el.value = opt.value;
32    }
33    
34}());
35// immediate function to preserve global namespace
36