Populate Drop Down List using jquery from textbox

I have a textbox whose id is other and I want to populate this textbox value into drop down list This is javascript I am using to populate... but this is not working.. Any suggestion will be appreciated...!! I want to do like this:- http://viralpatel.net/blogs/demo/dynamic-combobox-listbox-dropdown-in-javascript.html

<SCRIPT language="javascript"> 
function addCombo() {
    var textb = $('#other').attr('id');
    var combo = $('#category').attr('id');
    alert(combo);

    var option = document.createElement("option");
    option.text = $('#other').val();
    alert(optio开发者_Python百科n.text);
    option.value = $('#other').val();
    try {
        combo.add(option, null); //Standard 
    }catch(error) {
        combo.add(option); // IE only
    }
    textb.value = "";
}
</SCRIPT>

This is the code of drop down list

<td>Category</td>
                    <td><select class="size" id="category" name="category" width="30px">
                    <option width="30px" value="" selected="selected" >Select</option>
                    <option value="food">Food</option>
                        <option value="rent">Rent</option>
                        <option value="gas">Gas</option>
                        <option value="enter">Entertainment</option>
                        <option value="grocery">Grocery</option>
                        <option value="general">General</option>
                        <option value="other">Other</option></select></td>
                        </tr>
                        <tr>
                        <td>Other</td>
                        <td><input type="text" id="other" name="other"/></td>
                        <td><input type="button" data-role="button" value="Add" onclick="addCombo()"></td>
                        </tr>

I believe its because

var textb = $('#other').attr('id');
var combo = $('#category').attr('id');

Aren't you assigning id's of these elements to variables, instead of elements?
I mean... is textb really a input element after this code executes, or is it just a string "other"?

Try this:

var textb = $('#other');
var combo = $('#category');

Edit:

function addCombo() {
    var textb = document.getElementById("other");
    var combo = document.getElementById("category");

    var option = document.createElement("option");
    option.text = textb.value;
    option.value = textb.value;
    try {
        combo.add(option, null); //Standard 
    }catch(error) {
        combo.add(option); // IE only
    }
    textb.value = "";
}

Since you're already using jQuery:

function addCombo() {
    var optName = $("#other").attr("value");
    $('#category').append("<option value='"+ optName + "'>" + optName  + "</option>");
    $("#other").attr("value", "");
}