How to create or add cookie value by javascript?

<script type="text/javascript">
function setCookie(c_name,value,exdays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate() + exdays);
var c_value=escape(value) + ((exdays==null) ? "" : "; expires="+exdate.toUTCString());
document.cookie=c_name + "=" + c_value;
}

call this function to create cookie  like below
setCookie("cookie_name",value,365);
if you dont want delete a cookie after a several time then place 0 zero on exdays(356)
</script>