Devise a code in javascript to receive a positive number and output the product of its final five digits $($or its final digits, if they all number less than five$).$ For instance, if the input is $12811,$ the program should output $16,$ because $1*1*8*2*1$ is $16.$ Another example, if the input is $23$ the program should output $6.$ However, if the input is $712811$ the program should output $16,$ as the first digit will be ignored.