I had take date into a variable like below.
var todayDate = new Date();
After this I am assigning todayDate to another variable:
 var yesterdayDate = todayDate;
 yesterdayDate.setDate(yesterdayDate.getDate() - 1);
After this I am assigning todayDate to another variable:
 var next30daysDate = todayDate;
 next30daysDate.setDate(next30daysDate.getDate() + 29);
How should I keep todayDate constant for above two variables. in my case it is chnging for very variable.
 
    