求正则匹配字符串中只出现过一次的字符?
如"aabbccaaddeeccabfcae"匹配"f"
不知可不可以?
[解决办法]
视乎只能靠遍历吧。。。

    var s = "aabbccaaddeeccabfcae";
    var kv = {}, chr = false
    s.replace(/[a-z]/g, function ($0) { if (kv[$0] == undefined) { chr = $0;  kv[$0] = 1 } });
    alert(chr)