title: javascript textarea scrollTop
body: <p>I'm trying to enable checkbox once the user reads all the agreement. Yet, well, I've tried googling with no avail and also confused. I'm trying to get the "real" end of scrollTop, but due to different rendering engines (gecko, webkit, blah blah? ) a fixed value won't work. </p>
  
  <p>This is part of my learning so please avoid posting solutions with libraries. </p>
  
  <p>Any suggestions? </p>