javascript delete cookie, set cookie

function delete_cookie(name){
	document.cookie=name+'=; expires=Thu, 01 Jan 1970 00:00:01 GMT;';
}

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);
}