var speed = 16; //速度数值越大速度越慢

document.getElementById('demo2').innerHTML = document.getElementById('demo1').innerHTML;
document.getElementById('demo2').scrollLeft = document.getElementById('demo2').scrollWidth;
function Marqueetoleft() {
  if ((document.getElementById('demo2').offsetWidth - document.getElementById('demo').scrollLeft) <= 0) {
    document.getElementById('demo').scrollLeft -= document.getElementById('demo1').offsetWidth;
  } else {
    document.getElementById('demo').scrollLeft += 1;
  }
}

function MarqueetoleftFast() {
	if((document.getElementById('demo2').offsetWidth - document.getElementById('demo').scrollLeft) < (document.getElementById('demo').offsetWidth+12)){
		document.getElementById('demo').scrollLeft = document.getElementById('demo').scrollLeft + document.getElementById('demo').offsetWidth+12 - document.getElementById('demo1').offsetWidth;
	} else {
		//alert(document.getElementById('demo').offsetWidth);
  	document.getElementById('demo').scrollLeft += document.getElementById('demo').offsetWidth+12;
	}
}

function Marqueetoright() {
  if (document.getElementById('demo').scrollLeft <= 0) {
    document.getElementById('demo').scrollLeft += document.getElementById('demo1').offsetWidth;
  } else {
  	document.getElementById('demo').scrollLeft--;
  }
}

function MarqueetorightFast() {
	if(document.getElementById('demo').scrollLeft <= document.getElementById('demo').offsetWidth+12){
		document.getElementById('demo').scrollLeft = document.getElementById('demo').scrollLeft - (document.getElementById('demo').offsetWidth+12) + document.getElementById('demo1').offsetWidth;
	} else {
  	document.getElementById('demo').scrollLeft -= document.getElementById('demo').offsetWidth+12;
	}
}
MyMar = setInterval(Marqueetoleft, speed);