title: moments how to get the last weekday of the last month(december)
body: <p>i'm following this guide <a href="https://stackoverflow.com/questions/39446035/get-the-first-weekday-of-the-month-with-moment-js">Get the First Weekday of the Month with moment.js</a></p>
  
  <p>and it works fine to get the first weekday of the first month(January)</p>
  
  <p>but, when i'm trying to use the opposite. i'm getting the last weekday of the month that will be December. i try to change the add in minus and sub but not working</p>