JS 判断中英文字符长度

function strlen(str) {
        var len = 0;
        for (var i = 0; i < str.length; i++) {
            var c = str.charCodeAt(i);
            //单字节加1
            if ((c >= 0x0001 && c <= 0x007e) || (0xff60 <= c && c <= 0xff9f)) {
                len++;
            }
            else {
                len += 2;
            }
        }
        return len;
    }