Javascript - How to set and get cookie variable

This code searches for cookie value by key:

function get_cookie(Name) {
var search = Name + '='
var returnvalue = '';

if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
// if cookie exists
if (offset != -1) {
offset += search.length
// set index of beginning of value
end = document.cookie.indexOf(";", offset);
// set index of end of cookie value
if (end == -1) end = document.cookie.length;
returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

Setting cookie value:
document.cookie=key+"=" +value;