function createCookie(name, value, days) {
    var expires = "";
    var date = new Date();
    if (days) {
        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
        expires = "; expires=" + date.toGMTString();
    }
    document.cookie = name + "=" + value + expires + "; path=/";
}
function readCookie(name) {
    var nameEQ = name + "=";
    var allCookies = document.cookie.split(";");
    allCookies.forEach(function (cookie) {
        while (cookie.charAt(0) === " ") {
            cookie = cookie.substring(1, cookie.length);
        }
        if (cookie.indexOf(nameEQ) === 0) {
            return cookie.substring(nameEQ.length, cookie.length);
        }
    });
}
function eraseCookie(name) {
    createCookie(name, "", -1);
}

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

function readCookie(name) {
    var nameEQ = name + '=',
        allCookies = document.cookie.split(';'),
        i,
        cookie;
    for (i = 0; i < allCookies.length; i += 1) {
        cookie = allCookies[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);
}

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

function readCookie(name) {
    var nameEQ, ca, i, c;
    nameEQ = name + '=';
    ca = document.cookie.split(';');
    for (i = 0; i < ca.length; i += 1) {
        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);
}

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

function readCookie(name) {
	var nameEQ, ca, i, c;
	nameEQ = name + "=";
	ca = document.cookie.split(';');
	for (i = 0; i < ca.length; i += 1) {
		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);
}

http://www.quirksmode.org/js/cookies.html

Cleaned up (with the help of jslint.com)  versions of cookie handling functions

Cookie handling functions

javascript

JavaScript