var mouseIsDown = false;

window.onload = function()
{
  var e = document.getElementById('d1');

  document.onmousedown = docOnMousedown;
  document.onmouseup = docOnMouseup;
}

function docOnMousedown(e)
{
  mouseIsDown = true;
}
function docOnMouseup(e)
{
  mouseIsDown = false;
}