COOKIES:
- Cookies let you store user information in web pages.
- Cookies are data, stored in small text files, on computer.
- When a web server has sent a web page to a browser,
the connection is shut down, and the server forgets everything about the
user.
- Cookies were invented to solve the problem "how
to remember information about the user":
ü
When a user visits a web page, his name can
be stored in a cookie.
ü
Next time the user visits the page, the
cookie "remembers" his name.
- Cookies are saved in name-value pairs
When a browser request a
web page from a server, cookies belonging to the page is added to the request.
This way the server gets the necessary data to "remember" information
about users.
TO CREATE A COOKIE:
JavaScript
can create, read, and delete cookies with the document.cookie property.
With
JavaScript, a cookie can be created like this:
Document.cookie=”username=vinoth
kumar”;
By
default, the cookie is deleted when the browser is closed
We can
also add an expiry date to cookie:
document.cookie="username=Vinoth kumar; expires=Thu, 18 Dec 2014 12:00:00”;
With a
path parameter,we can tell the browser what path the cookie belongs to.
By
default, the cookie belongs to the current page.
document.cookie="username=Vinoth kumar; expires=Thu, 18 Dec 2014
12:00:00 ; path=/";
TO READ A COOKIE:
var x =
document.cookie;
TO CHANGE A COOKIE:
We can
change a cookie the same way as we create it:
document.cookie="username=SAN SUI; expires=Thu, 18 Dec 2014 12:00:00 ;
path=/";
TO DELETE A COOKIE:
Deleting
a cookie is very simple. Just set the expires parameter to a passed date:
document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 ";
Note: we don't need to specify a cookie value when you delete a
cookie.
Example:
In the example , we will
create a cookie that stores the name of a visitor.
The first time a visitor
arrives to the web page, he will be asked to fill in his name. The name is then
stored in a cookie.
The next time the visitor
arrives at the same page, he will get a welcome message.
For the example we will
create 3 JavaScript functions:
1.
A function to set a cookie value
2.
A function to get a cookie value
3.
A function to check a cookie value
<html>
<head>
<script>
function
setCookie(cname,cvalue,exdays) {
var d = new Date();
d.setTime(d.getTime() +
(exdays*24*60*60*1000));
var expires = "expires=" +
d.toGMTString();
document.cookie =
cname+"="+cvalue+"; "+expires;
}
function
getCookie(cname) {
var name = cname + "=";
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);
if (c.indexOf(name) == 0) {
return c.substring(name.length,
c.length);
}
}
return "";
}
function
checkCookie() {
var user=getCookie("username");
if (user != "") {
alert("Welcome again " +
user);
} else {
user = prompt("Please enter your
name:","");
if (user != "" && user
!= null) {
setCookie("username",
user, 30);
}
}
}
</script>
</head>
<body
onload="checkCookie()">
</body>
</html>
Reference:
http://www.w3schools.com
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