<textarea rows="5" onscroll="deplace()">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quisquam at praesentium ducimus velit consectetur tempore fugit odit delectus placeat perferendis id eveniet fuga! Asperiores eius quidem optio porro iusto repellendus.</textarea><br>

<p>Message : <span id="info3"></span></p>

span{
  color:red; 
}

input{
  color:green
}

bol=false;

function deplace(){
  bol = !bol; 
  if(bol){document.getElementById('info3').innerHTML+='Scroll actif - '
         }else{
    document.getElementById('info3').innerHTML+=''}
}