The example you give is false. Valid parentheses are not just defind by starting with an open paren ( and ending with a closed paren ). They have to be matched. Is )( valid?`

Convert is in the System namespace, so you have to define using System; at the top of your solution. Note that you can also use int.Parse(string).

array2.Length is undefined and JS would never complain you about that, you should use array2.length

An advice: Don't start your programmming career with JS.