When you set a cookie you should specify an expire time and a path. If you don’t specify a path the cookie is accessible only by the current page.
As per the MDN Web docs:
Cookie path – If not specified, defaults to the current path of the current document location.
An example of setting a maximum age and path:
// Set cookie with path. document.cookie = "theme=dark; Max-Age=604800; path=/";
By setting path=/, the cookie is now available from every page in your application/domain. If you do not specify the path then the current cookie is saved just for the current page and you can’t access it from other pages.
If using this API, then you can create a cookie, valid across the entire site with the following code:
// Set cookie. Cookies.set('name', 'value');