how to get length of substring in Regular Expression JavaScript

how to get length of substring in Regular Expression JavaScript

here is my regular expression
/^[a-zA-Z0-9-]{40}([a-zA-Z0-9-]{3}2[a-zA-Z0-9-]{12}){2,10}$/
There will be one condition: the length of every string after first 40
characters must be 16 characters. This 16 characters string will be non
repeating and minimum of 2 times and maximum of 10 times. So i want to get
the length of this sub-string which should be 16.