WEB存储
一、概述
HTML5 web storage, a better local storage than cookies.
What is HTML5 Web Storage?
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.
Browser Support
Web storage is supported in Internet Explorer 8+, Firefox, Opera, Chrome, and Safari.
Note: Internet Explorer 7 and earlier versions, do not support web storage.
二、使用方法
localStorage and sessionStorage
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.
Example
localStorage.lastname="Smith";
document.getElementById("result").innerHTML="Last name: "
+ localStorage.lastname;
Try it yourself »
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.
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:
Example
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).";
Try it yourself »
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.
The following example counts the number of times a user has clicked a button, in the current session:
Example
if (sessionStorage.clickcount)
{
sessionStorage.clickcount=Number(sessionStorage.clickcount)+1;
}
else
{
sessionStorage.clickcount=1;
}
document.getElementById("result").innerHTML="You have clicked the button " + sessionStorage.clickcount + " time(s) in this session.";