Use the selectedIndex
property:
document.getElementById("Mobility").selectedIndex = 12; //Option 10
Alternate method:
Loop through each value:
//Get select object
var objSelect = document.getElementById("Mobility");
//Set selected
setSelectedValue(objSelect, "10");
function setSelectedValue(selectObj, valueToSet) {
for (var i = 0; i < selectObj.options.length; i++) {
if (selectObj.options[i].text== valueToSet) {
selectObj.options[i].selected = true;
return;
}
}
}