Problem Solved By The Feature

If you want to cache a page in different variants on the server side, e.g. a variant for logged-in and non-logged-in users, or for different viewports, this cannot be implemented with one cache per URL.

In such scenarios, the page cached in another variant would lead to a content shift or flickering when loading the page.

Solution

Provide a factory method that allows to modify the key used to store the cache.

For example:

    const isr = new ISRHandler({
        indexHtml,
        invalidateSecretToken: process.env['INVALIDATE_TOKEN'] || 'MY_TOKEN',
        enableLogging: false,
        cacheKeyFactory: (req: Request) => {
            if (req.cookies && req.cookies.access_token) {
                return `${$req.url}%authenticated`;
            }
            return req.url;
        }
    });