JavaScript Cookies
A cookie is often used to identify a user.
What is a Cookie?
A cookie is a variable that is stored on the visitor's computer. Each
time the same computer requests a page with a browser, it will send the cookie
too. With JavaScript, you can both create and retrieve cookie values.
Examples of cookies:
- Name cookie - The first time a visitor arrives to your web page, he or
she must fill in her/his name. The name is then stored in a cookie. Next
time the visitor arrives at your page, he or she could get a welcome message
like "Welcome John Doe!" The name is retrieved from the stored cookie
- Password cookie - The first time a visitor arrives to your web page, he
or she must fill in a password. The password is then stored in a cookie.
Next time the visitor arrives at your page, the password is retrieved from
the cookie
- Date cookie - The first time a visitor arrives to your web page, the
current date is stored in a cookie. Next time the visitor arrives at your
page, he or she could get a message like "Your last visit was on Tuesday
August 11, 2005!" The date is retrieved from the stored cookie
Create and Store a Cookie
In this example we will create a cookie that stores the name of a visitor.
The first time a visitor arrives to the web page, he or she will be asked to
fill in her/his name. The name is then stored in a cookie. The next time the
visitor arrives at the same page, he or she will get welcome message.
First, we create a function that stores the name of the visitor in a cookie variable:
function setCookie(c_name,value,expiredays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate()+expiredays);
document.cookie=c_name+ "=" +escape(value)+
((expiredays==null) ? "" : ";expires="+exdate.toGMTString());
} |
The parameters of the function above hold the name of the cookie, the value of the cookie, and the number of days until the cookie expires.
In the function above we first convert the number of days to a valid date, then we add the number of days until the cookie should expire.
After that we store the cookie name, cookie value and the expiration date in the document.cookie object.
Then, we create another function that checks if the cookie has been set:
function getCookie(c_name)
{
if (document.cookie.length>0)
{
c_start=document.cookie.indexOf(c_name + "=");
if (c_start!=-1)
{
c_start=c_start + c_name.length+1;
c_end=document.cookie.indexOf(";",c_start);
if (c_end==-1) c_end=document.cookie.length;
return unescape(document.cookie.substring(c_start,c_end));
}
}
return "";
} |
The function above first checks if a cookie is stored at all in the document.cookie object. If the document.cookie object holds some cookies, then
check to see if our specific cookie is stored. If our cookie is found, then return the value, if not - return an empty string.
Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not set it will display a prompt box, asking for the
name of the user:
function checkCookie()
{
username=getCookie('username');
if (username!=null && username!="")
{
alert('Welcome again '+username+'!');
}
else
{
username=prompt('Please enter your name:',"");
if (username!=null && username!="")
{
setCookie('username',username,365);
}
}
} |
All together now:
Example
<html>
<head>
<script type="text/javascript">
function getCookie(c_name)
{
if (document.cookie.length>0)
{
c_start=document.cookie.indexOf(c_name + "=");
if (c_start!=-1)
{
c_start=c_start + c_name.length+1;
c_end=document.cookie.indexOf(";",c_start);
if (c_end==-1) c_end=document.cookie.length;
return unescape(document.cookie.substring(c_start,c_end));
}
}
return "";
}
function setCookie(c_name,value,expiredays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate()+expiredays);
document.cookie=c_name+ "=" +escape(value)+
((expiredays==null) ? "" : ";expires="+exdate.toGMTString());
}
function checkCookie()
{
username=getCookie('username');
if (username!=null && username!="")
{
alert('Welcome again '+username+'!');
}
else
{
username=prompt('Please enter your name:',"");
if (username!=null && username!="")
{
setCookie('username',username,365);
}
}
}
</script>
</head>
<body onload="checkCookie()">
</body>
</html> |
Try it yourself »
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The example above runs the checkCookie() function when the page loads.
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