How to convert varchar datatype to date in javascript..?

Hi.,
I have two columns with varchar datatype namely, FromRange and ToRange  in my table.
I can store any kind of data like, Numbers, test,Date etc..... I should not change that datatype.....
If i store date in that column like., it store like the varcahr like 19/10/2012(FromRange) and 19/10/2013(ToRange).
This date is store for settings for a Questions, while user enter answer, they should enter date between the FromRange and ToRange date .
So i load this date from Code behind and send to javascript function via Json. In that javascript function,
I convert this date text to date like.,
var FromDate = new Date(pSettings.FromRange);
var ToDate = new Date(pSettings.ToRange);
alert(FromDate); ----------------    It gives alert like, InvalidDate. Same as for ToRang ...