encoding in javascript

hi!
someone can tell me how to encode a menulist value?
explain: with the function

[U]trimString(getelementbyid(“searchbox”).value)[/U]
im getting the string i wrote in the menulist, but now if im writing ” ” its give me “+”, or “@” to %2540, or “#$”%^{^&””} to “%2523%2524%2522%2525%255e%2526%2522%255c”…

how to cange it back?
thx!!

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