Filling up combo by selecting values of multiple combo in JS

[computerzworld]

Hello All,
I want to fill up the combo by selecting values and text of multiple combo in Javascript. How can I do this? Please help me. Thanks in advance.

[rulian]

Can you elaborate or give an example?

[computerzworld]

I am having one multiple selection box which contains the values coming from database. And I want to fill up the second combo(single selection combo) from that because what is the exact requirement is that user can select multiple options & from that one will be default option. So, that what I require exactly is to select multiple combo & fill out its values in second one. And if user unselects some values the values in the second combo will also be removed.