html5本地存储 local storage

2013-11-06 22:15 youxin 阅读(545) 评论(0) 编辑收藏举报

HTML5 web storage, a better local storage than cookies.

With HTML5, web pages can store data locally within the user's browser.

Earlier, this was done with cookies. However, Web Storage is more secure and faster. The data is not included with every server request, but used ONLY when asked for. It is also possible to store large amounts of data, without affecting the website's performance.

The data is stored in key/value pairs, and a web page can only access data stored by itself.

html5 提供2 两种在客户端存储数据的办法:

There are two new objects for storing data on the client:

localStorage - stores data with no expiration date
sessionStorage - stores data for one session

Before using web storage, check browser support for localStorage and sessionStorage:

if(typeof(Storage)!=="undefined")
{
// Yes! localStorage and sessionStorage support!
// Some code.....
}
else
{
// Sorry! No web storage support..
}

The localStorage Object

The localStorage object stores the data with no expiration date. The data will not be deleted when the browser is closed, and will be available the next day, week, or year.

localStorage 方法存储的数据没有时间限制。第二天、第二周或下一年之后，数据依然可用。

如何创建和访问 localStorage：

localStorage.lastname="Smith";
document.getElementById("result").innerHTML="Last name: "
+ localStorage.lastname;

Example explained:

Create a localStorage key/value pair with key="lastname" and value="Smith"
Retrieve the value of the "lastname" key and insert it into the element with id="result"

Tip: Key/value pairs are always stored as strings. Remember to convert them to another format when needed.

key/value总是作为字符串存储，记住需要时转换他们。

The following example counts the number of times a user has clicked a button. In this code the value string is converted to a number to be able to increase the counter:

<script>
function clickCounter()
{
if(typeof(Storage)!=="undefined")
  {
  if (localStorage.clickcount)
    {
    localStorage.clickcount=Number(localStorage.clickcount)+1;
    }
  else
    {
    localStorage.clickcount=1;
    }
   document.getElementById("result").innerHTML="You have clicked the button " + localStorage.clickcount + " time(s).";
  }
else
  {
  document.getElementById("result").innerHTML="Sorry, your browser does not support web storage...";
  }
}
</script>
</head>
<body>
<p><button onclick="clickCounter()" type="button">Click me!</button></p>
<div id="result"></div>

The sessionStorage Object

The sessionStorage object is equal to the localStorage object, except that it stores the data for only one session. The data is deleted when the user closes the browser window.

sessionStorage当用户关闭浏览器后，删除。

The following example counts the number of times a user has clicked a button, in the current session:

<script type="text/javascript">
if (sessionStorage.pagecount)
  {
  sessionStorage.pagecount=Number(sessionStorage.pagecount) +1;
  }
else
  {
  sessionStorage.pagecount=1;
  }
document.write("Visits "+sessionStorage.pagecount+" time(s) this session.");
</script>