效果如下：
demo code:
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<input onclick="addcokie()" type="button"value="创建cookie"/>
<input onclick="readcokie()" type="button"value="读取cookie"/>
<h1 id="h11"></h1>
</body>
</html>
<script>
function addcokie(){
var exp=new Date();
exp.setTime(exp.getTime()+7*24*60*60*1000);
document.cookie="usename=yanbo;"+"expires="+exp.toGMTString();
}
function readcokie(){
h11.innerHTML=document.cookie;
}
</script>