Service Workers

A client-side programmable proxy that intercepts network requests to enable offline functionality and background synchronization.

Service Workers act as a persistent bridge between the browser and the network, running on a separate thread from the main UI. By leveraging the Fetch API and Cache storage, these scripts allow developers to intercept every outgoing request (HTTP/HTTPS) and provide instant responses from local assets. They power Progressive Web Apps (PWAs) with features like Push API notifications and Background Sync, ensuring web applications remain functional under 2G speeds or total offline conditions. Implementation requires a secure context (HTTPS) and a defined scope to manage lifecycle events like installation and activation.

https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API