stopgo.js

javascript:(function(){

var body = window.document.body,
    hh = body.scrollTop,
    interval = null,
    style_div = "font-family:helvetica;border-radius:5px;border:1px solid #222;border-bottom: 2px solid #111;padding:10px;position:fixed;top:20px;left:20px;background:#555",
    style_link = "padding: 5px;background:#222;color:#eee;text-decoration:none;margin:5px;",
    tpl = "<div id='stoppy' style='" + style_div + "'><a style='" + style_link + "' href='#' id='start-btn'>start</a> \
    <a  style='" + style_link + "' href='#' id='stop-btn'>stop</a>";

body.insertAdjacentHTML('beforeend', tpl);
var stoppy = document.getElementById('stoppy');
stoppy.addEventListener('click', function (e) {
  e.preventDefault(); e.stopPropagation();
  if (e.target.id === 'start-btn') start();
  else if (e.target.id === 'stop-btn') stop();
}, false);

function start(){
  interval = setInterval(function(){
    body.scrollTop += 500;
  }, 1400);
};

function stop(){
    clearInterval(interval);
}
}(window));