var speed_k = 800; //pixels per second for 1000 pixels height
var steps = 20; //number of steps for jump

var c = 0; var height = 1000;  var step_height;  var step_time;  function MoveUp()  {  c = 0;  height = document.body.scrollTop+300;    speed = speed_k*(height/1000);     step_height = height/steps;     step_time = (height/speed)/steps;     _MoveUp();   }   function _MoveUp(){ c++; if(c<steps) { window.scrollBy(0,-step_height); setTimeout(function () { _MoveUp()}, step_time);  }   }