var div1=document.getElementById("div1");
var iSpeedX=6;
var iSpeedY=8;
setInterval(function(){
  var l=div1.offsetLeft+iSpeedX;
  var t=div1.offsetTop+iSpeedY;
  if(t>=document.documentElement.clientHeight-div1.offsetHeight){
    iSpeedY*=-1; //速度反向
    t=document.documentElement.clientHeight-div1.offsetHeight; //超出下边界时，把它拉回到下边界，不然右边滚动条会闪动出现一下
  }
  else if(t<=0){
    iSpeedY*=-1;
    t=0;
  }
  if(l>=document.documentElement.clientWidth-div1.offsetWidth){
    iSpeedX*=-1;
    l=document.documentElement.clientWidth-div1.offsetWidthl;
  }
  else if(l<=0){
    iSpeedX*=-1;
    l=0;
  }
  div1.style.left=l+'px';
  div1.style.top=t+'px';
},30);

setInterval(function(){
  iSpeedY+=3;
  var l=div1.offsetLeft+iSpeedX;
  var t=div1.offsetTop+iSpeedY;
  if(t>=document.documentElement.clientHeight-div1.offsetHeight){
    iSpeedY*=-0.8;
    iSpeedX*=0.8; //横向速度也要变慢，否则碰到地面时会停不下来
    t=document.documentElement.clientHeight-div1.offsetHeight;
  }
  else if(t<=0){
    iSpeedY*=-1;
    iSpeedX*=0.8;
    t=0;
  }
  if(l>=document.documentElement.clientWidth-div1.offsetWidth){
    iSpeedX*=-0.8;
    l=document.documentElement.clientWidth-div1.offsetWidthl;
  }
  else if(l<=0){
    iSpeedX*=-0.8;
    l=0;
  }
  if(Math.abs(iSpeedX)<1){ //解决小数的问题，因为假如速度是小数，正的没问题，100(iSpeed=0.5)-->100.5-->100，负的100(iSpeed=-0.5)--->99.5-->99，可能会出现x轴反向时滑行
    iSpeedX=0;
  }
  if(Math.abs(iSpeedY)<1){
    iSpeedY=0;
  }
  div1.style.left=l+'px';
  div1.style.top=t+'px';
},30);

window.onload=function ()
{
  var oDiv=document.getElementById('div1');
  var lastX=0;
  var lastY=0;
  oDiv.onmousedown=function (ev)
  {
    var oEvent=ev||event;
    var disX=oEvent.clientX-oDiv.offsetLeft;
    var disY=oEvent.clientY-oDiv.offsetTop;
    document.onmousemove=function (ev)
    {
      var oEvent=ev||event;
      var l=oEvent.clientX-disX;
      var t=oEvent.clientY-disY;
      oDiv.style.left=l+'px';
      oDiv.style.top=t+'px';
      iSpeedX=l-lastX; //拖拽结束时的速度
      iSpeedY=t-lastY;
      lastX=l; //更新上一个点的位置
      lastY=t;
    };
    document.onmouseup=function ()
    {
      document.onmousemove=null;
      document.onmouseup=null;
      startMove(); //拖拽结束时执行
    };
    clearInterval(timer);
  };
};
var timer=null;
var iSpeedX=0;
var iSpeedY=0;
function startMove()
{
  clearInterval(timer);
  timer=setInterval(function (){
    var oDiv=document.getElementById('div1');
    iSpeedY+=3;
    var l=oDiv.offsetLeft+iSpeedX;
    var t=oDiv.offsetTop+iSpeedY;
    if(t>=document.documentElement.clientHeight-oDiv.offsetHeight)
    {
      iSpeedY*=-0.8;
      iSpeedX*=0.8;
      t=document.documentElement.clientHeight-oDiv.offsetHeight;
    }
    else if(t<=0)
    {
      iSpeedY*=-1;
      iSpeedX*=0.8;
      t=0;
    }
    if(l>=document.documentElement.clientWidth-oDiv.offsetWidth)
    {
      iSpeedX*=-0.8;
      l=document.documentElement.clientWidth-oDiv.offsetWidth;
    }
    else if(l<=0)
    {
      iSpeedX*=-0.8;
      l=0;
    }
    if(Math.abs(iSpeedX)<1)
    {
      iSpeedX=0;
    }
    if(Math.abs(iSpeedY)<1)
    {
      iSpeedY=0;
    }
    if(iSpeedX==0 && iSpeedY==0 && t==document.documentElement.clientHeight-oDiv.offsetHeight)
    {
      clearInterval(timer);
    }
    else
    {
      oDiv.style.left=l+'px';
      oDiv.style.top=t+'px';
    }
    document.title=iSpeedX;
  }, 30);
}