Weekly Tips : Learn How to Use Cookie with Javascript

Introduction

This is my very first weekly tips for web design and development. From now on, I'll be posting it every week, and will cover all sort of interesting, helpful web design and development tips and tricks.

"In computing, a cookie (also tracking cookie, browser cookie, and HTTP cookie) is a small piece of text stored on a user's computer by a web browser. A cookie consists of one or more name-value pairs containing bits of information such as user preferences, shopping cart contents, the identifier for a server-based session, or other data used by websites." - Wikipedia - HTTP Cookie

Yes, we'll look into how to manipulate cookies using Javascript. Just in case f you have no ideas what cookies can do, below are the two major usages:

Store authentication/session: Have you notice that remember me checkbox under the login box? It uses cookie to remember you. It stores your session details so that you don't have to login when you visit the website again.
Store data: You can use cookie to store data in client's computer. For example, Displaying a "welcome back" message or automatically fill in the username field. Or you can use it to remember the position of the current selected menu item, selected tab or position of elements

Advantages

Cookies do not use server resources since it stores in client's computer.
Expiry date of cookies can be configured.
Easy to implement.

Diadvantages

Users can delete a cookies.
Browsers can be set to decline cookies (By default, all browsers accept cookies).
Cookie stores data in plain text thus a potential security threat.
It can store huge amount of data

Create, Modify and Erase Cookie

We have to understand how it works before we can go further, the structure of cookie is simple, it's made of:

Name-value pair which stores the data.
Expiry date, after which time the entry will be deleted.
Web domain and path that the cookie should be associated with.

/* assume today date is 2009-09-09 */
/* Create a cookie that will expire 2 days later */
document.cookie = "name=kevin; expires=Fri, 11-Sep-2009 23:59:59 GMT; path=/";

/* Reassign value */
document.cookie = "name=queness; expires=Fri, 11-Sep-2010 23:59:59 GMT; path=/";

/* Erase a cookie, put a past date */
document.cookie = "name=queness; expires=Fri, 08-Sep-2009 23:59:59 GMT; path=/";

Cookie Functions to Make Your Life Easier

Kudos to Quirksmode.org, they have created these functions to create, read and erase cookie easily. We don't even have to remember the GMT date format, we just have to set number of days and it will do the rest for us. Pretty good huh?

function createCookie(name,value,days) {
	if (days) {
		var date = new Date();
		date.setTime(date.getTime()+(days*24*60*60*1000));
		var expires = "; expires="+date.toGMTString();
	}
	else var expires = "";
	document.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) {
	var nameEQ = name + "=";
	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,c.length);
		if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
	}
	return null;
}

function eraseCookie(name) {
	createCookie(name,"",-1);
}

A Simple Implementation Menu

Alright, a really simple real implementation, it remembers which menu item you have just clicked, and the script assign a selected class to it. It highlights the current menu item.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" 
	"http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
	<title>untitled</title>
	<script type="text/javascript" src="js/jquery-1.3.1.min.js"></script>
	<link type="text/css" rel="stylesheet" href=""/>
	<script>
	
	$(document).ready(function () {

		//for debugging purpose, so that you can see what is in the menu cookie
		$('#debug').html('Cookie Content : ' + readCookie('menu'));

		//if cookie menu exists
		if (readCookie('menu')) {
			
			//loop through the menu item
			$('#menu a').each(function () {
				//match the correct link and add selected class to it
				if ($(this).html() == readCookie('menu')) $(this).addClass('selected');
			});	
		}

		$('#menu a').click(function () {

			//Set the cookie according to the text in the link
			createCookie('menu', $(this).html(),1);
		});
		
	});


	/* Cookie Function */
	function createCookie(name, value, days) {
		if (days) {
			var date = new Date();
			date.setTime(date.getTime()+(days*24*60*60*1000));
			var expires = "; expires="+date.toGMTString();
		}
		else var expires = "";
		document.cookie = name+"="+value+expires+"; path=/";
	}

	function readCookie(name) {
		var nameEQ = name + "=";
		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,c.length);
			if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
		}
		return null;
	}

	function eraseCookie(name) {
		createCookie(name,"",-1);
	}

	</script>
	
	<style>
	ul {
		padding:0;
		margin:0;
		list-style:none;
	}
	
		li {
			float:left;
			margin:0 10px;

		}
		
		li a {
			border-bottom:3px solid #ccc;	
			text-decoration:none;
			display:block;
			color:#666;
		}
		
		li a:hover {
			border-bottom:3px solid #000;					
		}
		
		li a.selected {
			border-bottom:3px solid #000;					
		}
		
	.clear {
		clear:both;	
	}
	</style>
</head>
<body>

<ul id="menu">
<li><a href="index.html">Home</a></li>
<li><a href="index.html">Tips</a></li>
<li><a href="index.html">Porfolios</a></li>
<li><a href="index.html">About</a></li>
<li><a href="index.html">Contact</a></li>
</ul>

<div class="clear"></div>

<br/><br/>
<div id="debug"></div>

</body>
</html>

Copyright & Usage

The effects and techniques demonstrated in tutorials on Queness can be used in whatever manner you wish without attribution. You cannot copy whole tutorials (unless permission is given), either in English or translated to another language.

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