第九点关于cookie 的写法有缺陷

```
var setCookie = {
set: function(name, value) {
var Days = 30;
var exp = new Date();
exp.setTime(exp.getTime() + Days * 24 * 60 * 60 * 1000);
document.cookie = name + "=" + escape(value) + ";expires=" + exp.toGMTString();
}
}
```
#### 这种方式 在已存在 cookie键值对的情况下，只是 新增 一组cookie。并没有实现 setCookie 的功能。
建议改进为
```
/**
* 设置cookie
* @param {string} name 键名
* @param {string} value 键值
* @param {integer} days cookie周期
*/
function setCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime()+(days*24*60*60*1000));
var expires = "; expires="+date.toGMTString();
}else{
var expires = "";
}
document.cookie = name+"="+value+expires+"; path=/";
}
// 获取cookie
function getCookie(name) {
var nameEQ = name + "=";
var ca = document.cookie.split(';');
for(var i=0;i < ca.length;i++) {
var c = ca[i];
while (c.charAt(0)==' ') c = c.substring(1,c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
}
return null;
}
// 删除cookie
function deleteCookie(name) {
setCookie(name,"",-1);
}
```

Start by locating the setCookie implementation shown in the issue and inspect how it handles an existing cookie key. Compare its behavior with the proposed setCookie, getCookie, and deleteCookie examples; done means setting an existing key updates it and the related cookie operations work as described.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.