Select item in CascadingDropDown via JavaScript & invoke update - asp.net

Question

In code-behind I can do this to select something:
// Select item in first DropDownList
myCascadingDropDown_1.SelectedValue = itemValue_1+":::"+itemText_1;
// Select item in second DropDownList
myCascadingDropDown_2.SelectedValue = itemValue_2+":::"+itemText_2;
How can I do this in JavaScript?
(I'm aware, that I could search the list and set the selectedIndex property for each dropdown, but I have many items and i'm very lazy.)
EDIT:
npups answer works: I can select my desired item in the first dropdownlist. The problem is however, that new values based on that selected item (it is a CascadingDropDown, remember?) don't show in the second dropdown so I can't select anything there. I would need to somehow invoke the update method of the second dropdown manually: any suggestions?

Answer 1

I was able to solve this:
1) With npups suggestion I was able to set "myCascadingDropDown_1" to my desired value.
2) Using the
myCascadingDropDown_2.CascadingDropDownBehavior._onParentChange(null,
null);
method I was able to force the second dropdown to repopulate based on the new selected value of "myCascadingDropDown_1".
3) I wrote a timer to check periodically if the second dropdown has finished repopulation and set the desired value if it has (again using npups answer)..

Answer 2

Check this out:
<select id="foo">
<option value="bar">bar</option>
<option value="baz">baz</option>
<option value="bork">bork</option>
</select>
<script type="text/javascript">
var selectElem = document.getElementById('foo');
selectElem.value = 'baz';
</script>
Setting the value of the select element fixes that.
Firefox gets it right even if you just use the tags' content as values (instead of specifying a value in the option's value attribute). Not sure about other browsers.
EDIT, more stuff:
So there is some other select (or equivalent) that is updated by some harmonizing function when the first select changes?
Here, i have it in the first select's onchange. When the selected element is set with this "value-setting" technique, the onchange isn't triggered. Though, one can call the harmonizing function manually when you change the first select. I show two different ways (both in comments) below.
<select id="foo" onchange="harmonize();">
<option value="bar">bar</option>
<option value="baz">baz</option>
<option>bork</option>
</select>
<select id="foo2">
<option value="0">This</option>
<option value="1">That</option>
</select>
<script type="text/javascript">
var select0 = document.getElementById('foo');
var select1 = document.getElementById('foo2');
select0.value = 'baz';
// alternative 1: call harmonize();
// alternative 2: call select0.onchange();
function harmonize() {
if (select0.value==='baz') {
select1.value = '1';
}
else {
select1.value = '0';
}
}
</script>
I didn't bother to hide global variables etc. here, but of course that is a good idea.

Answer 3

you can also use myCascadingDropDown_2.set_SelectedValue(resultval, resultVal) instead of timer (item3)