关于正则

Question

        function CheckInput()
        {
            var s = document.getElementById("Text1").value;
            var patrn=eval("/^['aaa']$/");
            alert(patrn);
            alert(s);
            if (patrn.exec(s))
            {
                document.getElementById("Text2").value = document.getElementById("Text2").value + ",YES";
            }
            else
            {
                document.getElementById("Text2").value = document.getElementById("Text2").value + ",NO";
            }
        }
上面是我写的正则
当我在 Text1 中输入 a 时 Text2 中输出 YES
当我在 Text1 中输入 aa（或者更多字符） 时 Text2 中输出 NO请问怎么才能改为只有匹配 aaa  时 Text2 中输出 YES在线等