title: Add a symbol after every specified length in a textarea
body: <p>If a user type a long message in a textarea , I wish to add a symbol "#"(or whatever) when the message exceed every 100 characters in length.</p>
  
  <p>Such as..</p>
  
  <p><code>aa bb cc....(until 100 characters)#dd ee ff...(another 100 characters)#(continue...)</code></p>
  
  <p>I read <a href="https://stackoverflow.com/questions/8110313/add-points-after-every-3-digits-on-all-text-fields-with-js">this</a> solution...is it the similar way to do this function?</p>
  
  <p>Can someone give me some hints?Thankyou.</p>