Help ! with a calculator

im coding a Scientific Calculator by JavaScript so need a recommendation to perform a sin , cos , tan .

JS has a built-in Math object that has all those methods and more. Check it out:

im totally no that , just talk about the way to that like:
if i will perform math.cos(X) , will need the value x before but in face the user need to type cos(5) the the value will come next , hope i could explain