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

1.     <SCRIPT language="javascript"> 
2.     function addCombo() {
3.      var textb = $('#other').attr('id');
4.      var combo = $('#category').attr('id');
5.      alert(combo);
6.     
7.      var option = document.createElement("option");
8.      option.text = $('#other').val();
9.      alert(option.text);
10.      option.value = $('#other').val();
11.      try {
12.      combo.add(option, null); //Standard 
13.      }catch(error) {
14.      combo.add(option); // IE only
15.      }
16.      textb.value = "";
17.     }
18.     </SCRIPT>

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This is the code of drop down list

1.     <td>Category</td>
2.      <td><select class="size" id="category" name="category" width="30px">
3.      <option width="30px" value="" selected="selected" >Select</option>
4.      <option value="food">Food</option>
5.      <option value="rent">Rent</option>
6.      <option value="gas">Gas</option>
7.      <option value="enter">Entertainment</option>
8.      <option value="grocery">Grocery</option>
9.      <option value="general">General</option>
10.      <option value="other">Other</option></select></td>
11.      </tr>
12.                             <tr>
13.      <td>Other</td>
14.      <td><input type="text" id="other" name="other"/></td>
15.      <td><input type="button" data-role="button" value="Add" onclick="addCombo()"></td>
16.      </tr>