Set the selected index of a Dropdown using jQuery

Question

First of all - that selector is pretty slow. It will scan every DOM element looking for the ids. It will be less of a performance hit if you can assign a class to the element.

$(".myselect")

To answer your question though, there are a few ways to change the select elements value in jQuery

// sets selected index of a select box to the option with the value "0"
$("select#elem").val('0'); 

// sets selected index of a select box to the option with the value ""
$("select#elem").val(''); 

// sets selected index to first item using the DOM
$("select#elem")[0].selectedIndex = 0;

// sets selected index to first item using jQuery (can work on multiple elements)
$("select#elem").prop('selectedIndex', 0);

Just found this, it works for me and I personally find it easier to read.

This will set the actual index just like gnarf's answer number 3 option.

// sets selected index of a select box the actual index of 0 
$("select#elem").attr('selectedIndex', 0);

This didn't used to work but does now... see bug: http://dev.jquery.com/ticket/1474

Addendum

As recommended in the comments use :

$("select#elem").prop('selectedIndex', 0);

I'm writing this answer in 2015, and for some reason (probably older versions of jQuery) none of the other answers have worked for me. I mean, they change the selected index, but it doesn't actually reflect on the actual dropdown.

Here is another way to change the index, and actually have it reflect in the dropdown:

$('#mydropdown').val('first').change();

JQuery code:

$("#sel_status").prop('selectedIndex',1);

Jsp Code:

Status:
<select name="sel_status"
    id="sel_status">
    <option value="1">-Status-</option>
    <option>ALL</option>
    <option>SENT</option>
    <option>RECEIVED</option>
    <option>DEACTIVE</option>
</select>

I'm using

$('#elem').val('xyz');

to select the option element that has value='xyz'

You want to grab the value of the first option in the select element.

$("*[id$='" + originalId + "']").val($("*[id$='" + originalId + "'] option:first").attr('value'));

To select the 2nd option

$('#your-select-box-id :nth-child(2)').prop('selected', true);

---

Here we add the `trigger('change') to make the event fire.

$('#your-select-box-id :nth-child(2)').prop('selected', true).trigger('change');