<style type="text/css">

			*{

				margin:0px auto;

				padding:0px;

				}

        	#wai{

				width:100%;

				height:500px;

				}

			#nei_1{

				height:500px;

				background-color:blue;

				float:left;

				}

			#nei_2{

				height:500px;

				background-color:#6C0;

				float:left;

				}

			#anniu{

				width:50px;

				height:50px;

				background-color:red;

				position:absolute;

				top:225px;

				}

        </style>

    </head>

    <body>

    	<div id="wai">

        	<div id="nei_1" style="width:200px;" onclick="Hua()"></div>

            <div id="nei_2" style="width:700px;" onclick="Hui()"></div>

        </div>

        <div id="anniu" onclick="Hua()"  style="left:175px;"></div>

    </body>

    <script type="text/javascript">

    	//蓝色的长度变大

		//绿色的长度变小

		//红色框的位置

		var id;

		function Hua()

		{

			id = window.setInterval("Dong()",20);

		}

		//每一次调用一次，改变的样式

		function Dong()

		{

			//获取蓝色的元素

			var left = document.getElementById("nei_1");

			//获取蓝色的宽度

			var lw = left.style.width;	

			//判断宽度是否超出

			if(parseInt(lw.substr(0,lw.length-2))>700)

			{

				window.clearInterval(id);

				return;

			}

			//获取数字加2

			lw = parseInt(lw.substr(0,lw.length-2))+2;

			//修改样式

			left.style.width = lw+"px";

			//绿色的修改

			var right = document.getElementById("nei_2");

			var rw = right.style.width;

			rw = parseInt(rw.substr(0,rw.length-2))-2;

			right.style.width = rw+"px";

			//红色的修改

			var an = document.getElementById("anniu");

			var al = an.style.left;

			al = parseInt(al.substr(0,al.length-2))+2;

			an.style.left = al+"px";

		}

		var ad;

		function Hui()

		{

			ad = window.setInterval("Lai()",20);

		}

		function Lai()

		{

			//绿色的修改

			var right = document.getElementById("nei_2");

			var rw = right.style.width;

			if(parseInt(rw.substr(0,rw.length-2))>700)

			{

				window.clearInterval(ad);

				return;

			}

			rw = parseInt(rw.substr(0,rw.length-2))+2;

			right.style.width = rw+"px";

			//红色的修改

			var an = document.getElementById("anniu");

			var al = an.style.left;

			al = parseInt(al.substr(0,al.length-2))-2;

			an.style.left = al+"px";

			//获取蓝色的元素

			var left = document.getElementById("nei_1");

			//获取蓝色的宽度

			var lw = left.style.width;

			lw = parseInt(lw.substr(0,lw.length-2))-2;

			left.style.width = lw+"px";

		}

    </script>