Using Cookies in JavaScript

Update (February 23, 2007): I have updated the cookies functionality below to utilize flash storage if available and fall back to cookies if not available. See Cookies and Flash for local storage

Whether you like them or not, cookies are an easy way store simple user specific information across web pages and sessions. Here are the basic JavaScript methods to create (and update), read, or delete (CRUD) cookies with JavaScript.

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 cookies = document.cookie.split(';');
for(var i = 0; i < cookies.length;i++) {
 var cookie = cookies[i];
 while (cookie.charAt(0) == ' ') {
  cookie = cookie.substring(1, cookie.length);
 }
 if (cookie.indexOf(nameEQ) == 0) {
  return cookie.substring(nameEQ.length, cookie.length);
 }
}
return null;
}

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

Detailed explanation of code how this code works is available here. This script was originally written by Scott Andrew.