Web browser and server use the HTTP protocol to communicate and HTTP is a stateless protocol. But for a commercial website, it is required to maintain session information among different pages. For example, one user registration ends after completing many pages. But how to maintain user’s session information across all the WebPages. In many situations, using cookies is the most efficient method of remembering and tracking preferences, purchases, commissions, and other information required for better visitor experience or site statistics.
Your serve sends some data to the visitor's browser in the form or a cookie. The browser may accept the cookie. If it does, it is stored as a plain text record on the visitor’s hard drive. Now, when the visitor arrives at the nether page on your site, the browser sends the same cookie to the server for retrieval. Once retrieved, your server knows/remembers what was stored earlier. Cookies are a plain text data record of 5 variables –length fields
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Expires: The date the cookie will expire. If this is blank, the cookie will expire when the visitor quits the browser.
Domain: The domain name of your site.
Path: The path to the directory or webpage that set the cookie. This may be blank if you want to retrieve the cookie from any directory or page.
Secure: If this field contains the word ”secure” then the cookie may only be retrieved with a secure server. If this field is blank, no suck restriction exits.
Name=Value: Cookies are set and retrieved in the form of key and value pairs. Cookies were originally designed for CGI programming and cookies data is automatically transmitted between the web browser and webserver, so CGI scripts on the server can read and write cookies that are stored on the client. JavaScript can also manipulate cookies using the cookie property of the Document object. JavaScript can read, create, modify, and delete the cookie or cookies that apply to the current webpage.
The simplest way to create a cookie is to assign a string value to the document .cookie object, which looks like this
Syntax:
document.cookie=” key1=value1;kay2=value2;expires=date”; Here expires attribute is option .If you provide this attribute with a valid date or time then the cookie will expire at the given date or time and after that cookies value will not be accessible.
Note:
Cookie values may not include semicolons, commas, or whitespace,. For this reason, you may want to use the Javascript escape() function to encode the value before storing it in the cookie. If you do this, you will also have to use the corresponding unescape () function when you read the cookie value.
Example
Following is the example to set a customer name in the input cookie.
<html>
<head>
<script type=”text/javascript”>
<!—
Function WriteCookie ( )
{
If{document.myform.customer.value==””}
{ Alert{“Enter some value!”}; Return; }
Ccokievalue=escape{document.myform.customer.value} + “;” Document.cookie=”name”+cookievalue);
}
//-->
</script>
</head>
<body>
<form name =”myform” action=””>
Enter name:<input type=”text” name=”customer”/>
<input type=”button” value=”Set Cookie” onclick=”WriteCookie();”/>
</form>
</body>
</html>
Now your machine has a cookie called name. You can set multiple cookies using multiple key=value pairs separated by a comma. You will learn how to read this cookie in the next section.
Reading a cookie is just as simple as writing one because the value of the document .cookie object is the cookie. So you can use this string whenever you want to access the cookie.
The document cookie string will keep a list of name=value pairs separated by semicolons, where name is the name of a cookie and value is its string value. You can use strings’spli() function to break the string into key and values as follows.
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Example
Following is the example to get the cookies set in the previous section.
<html>
<head>
<script type=”text/javascript”>
<!—
Function Read Cookie{}
{
Var allcookies=document.cookie;
// Get all the cookies pairs in an array Cookiearray=allcookies.split(‘;’);
//Now take key-value pair out of this array
For {var i=0; i<cookiearray.lenght; i++}
{
Name = cookiearray[i].split{“=”} [0];
Value= cookiearray[i].split{“=”} [1];
Alert{key is :” + name +” and Value is :”+ value};
}
}
//-->
</script>
</head>
<body>
<form name =”myform” action=””>
<input type=”button” value=”Set Cookie” onclick=”ReadCookie();”/>
</form>
</body>
</html> Note: Here length is a method of Array class that returns the length of an array.
Note: There may be some other cookies already set on your machine. So above code will show you all the cookies set at your machine
You can extend the life of a cookie beyond the current browser session by setting an expiration date and saving the expiration date within the cookie. This can be done by setting the expires attribute to a date and time.
Example
The following is the example illustrates how to set a cookie expiration date after 1 month
<html>
<head>
<script type=”text/javascript”>
<!—
Function WriteCookie ( ) Var now=new Date{};
Now.setMonth{ now.getMonth{}+1};
Document.cookie=”name=”+cookievalue;
Document.cookie=”expires=”+now.getGMTString{}+”;” Alert{Setting Cookies :” +”name=”+ cookievalue };
</script>
</head>
<body>
<form name =”formname” action=””>
Enter name:<input type=”text” name=”customer”/>
<input type=”button” value=”Set Cookie” onclick=”WriteCookie();”/>
</form>
</body>
</html> Sometimes you will want to delete a cookie by setting expiration date one Month in past:
<html>
<head>
<script type=”text/javascript”>
<!—
Function WriteCookie ( ) Var now=new Date{};
Now.setMonth{ now.getMonth{} -1};
Cookievalue=escape{document.myform.customer.value}+”;”
Document.cookie=”name=”+cookievalue;
Document.cookie=”expires=”+now.getGMTString{}+”;” Alert{Setting Cookies :” +”name=”+ cookievalue };
}
//-->
</script>
</head>
<body>
<form name =”formname” action=””>
Enter name:<input type=”text” name=”customer”/>
<input type=”button” value=”Set Cookie” onclick=”WriteCookie();”/>
</form>
</body>
</html>Instead of setting a date, you can see a new time using the Time() function.
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