dropdownlist javascript change items

I can't find solution for this problem for very long time:

I have dropdownlists in Gridview. I need to dinamicly change content of dropdown on client with javascript. Ok, I know to do that. But the problem is when I send data to server changes in dropdownlist does not see. On server I have  old items. How can I change items in dropdown on client with javascript and than see that items on sever when postback data?


Thanks

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