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.