Coupon Generator with end of date use

Hello World,

I needed a coupon generator to generate about 200 unique coupon per day for my ecommerce and couldn't find one.

I never coded before the last 48h and didn't know what a variable,function or index was.

I watched a video about JavaScript for Beginner and went true the Zoho Deluge website to find functions.

I then created this one.

It gives about one and a half billion combination per day.

Should i worry about having a double coupon value happening?

Is there a way of avoiding it?

Should I worry about Brute Force?

Let me know if you have a better way of doing it.

//coupon
myList = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
x = randomNumber(1,36);
y = randomNumber(1,36);
z = randomNumber(1,36);
a = randomNumber(1,36);
firstPick = myList.subString(x,36);
firstChar = firstPick.subString(0,1);
secondPick = myList.subString(y,36);
secondChar = secondPick.subString(0,1);
thirdPick = myList.subString(z,36);
thirdChar = thirdPick.subString(0,1);
forthPick = myList.subString(a,36);
forthChar = forthPick.subString(0,1);
myrandnum = randomNumber(100,999);
currentDate = today;
oneYearFromNow = currentDate.addYear(1);
EndLifeOfCoupon = oneYearFromNow.toString("ddMMyy");
coupon = myrandnum + firstChar + secondChar + thirdChar + forthChar + EndLifeOfCoupon;
info coupon;