javascript正则表达式替换字符串

var reg = /^per_list(.*)[\d]{1,}(.*)/;
var str = "per_listAmtApril1.value";
var replaceStr = "";

var str2 = "per_listAmtApril1";
var replaceStr2 = "";

if(reg.test(str)) {
    replaceStr = str.replace(reg, "per_list$1" + new Date().getTime() + "$2");
}
console.log(replaceStr);

if(reg.test(str2)) {
    replaceStr2 = str2.replace(reg, "per_list$1" + new Date().getTime() + "$2");
}
console.log(replaceStr2);

结果：

per_listAmtApril1378043838654.value

per_listAmtApril1378043838656