Sometimes is useful to set a cookie with javascript. You can use the function below.

function Set_Cookie(name, value, expires, path, domain, secure )
{
var today = new Date();
today.setTime( today.getTime() );

if ( expires ) { expires = expires * 1000 * 60 * 60 * 24; }
var expires_date = new Date( today.getTime() + (expires) );
document.cookie = name + [...]