JSFiddle - React, Tailwind, and code Playground

HTML

<input id="user_join_date">
<input id="user_probation_end_date">

CoffeeScript

joinDate = $('#user_join_date')
joinDate.blur ->
  m=joinDate.val()
  console.log m
  splitdate = m.split('/')
  probationDate = new Date(splitdate[2], splitdate[0] - 1, splitdate[1])
  console.log probationDate
  myVar = new Date(probationDate.setMonth probationDate.getMonth())
  $('#user_probation_end_date').val(myVar)