add Option
HTML
<select id="s1">
<option value="red" style="color:red">red</option>
<option value="blue" style="color:blue">blue</option>
<option value="green">Green</option>
</select>
<input type="text" id="value">
<button id="b1">
Add
</button>
JavaScript
$("document").ready(function() {
$("#b1").click(function() {
var a = $("#value").val();
$("#s1").append($('<option>', {
value: a,
text: a
}));
});
})