replace的有关问题

replace的问题
var   dd= "fasdfsdfasdfasdfasdf "
var   cc= "f "

alert(dd.replace(eval( "/ "+cc+ "/gi "), ". "));

不用eval能实现相同的效果吗

[解决办法]
var reg = new RexExp(cc, "gi ");
alert(dd.replace(reg, ". "))