Alt-Svc allows the server to indicate to the web browser that a resource should be loaded on a different server. Because this is a persistent setting, it could be used to track users across websites if it is not correctly partitioned.write: async () => { // Clear Alt-Svc caching first. let responseText = ""; for (let i = 0; i < 3; ++i) { await fetch(altSvcOrigin + "/clear"); await sleepMs(100); }