HTML5 Web Storage

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.

There are several reasons to use client-side storage.

·         First, you can make your app work when the user is offline, possibly sync'ing data back once the network is connected again.

·         Second, it's a performance booster; you can show a large corpus of data as soon as the user clicks on to your site, instead of waiting for it to download again.

·         Third, it's an easier programming model, with no server infrastructure required. Of course, the data is more vulnerable and the user can't access it from multiple clients, so you should only use it for non-critical data, in particular cached versions of data that's also "in the cloud".

See "Offline": What does it mean and why should I care? for a general discussion of offline technologies, of which client-side storage is one component.

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 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;

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:

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.";

Good Luck...!!!