{Tutorial}HTML5 Application Cache.Step 33.

[MrHotFire]

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.

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.

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.

 

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:

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).";

 

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:

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."; 

 

 

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