Expo Server SDK for Node.js

The `expo-server-sdk` is a server-side library for Node.js environments, designed to facilitate the sending of push notifications to mobile applications built with Expo. It provides utilities for constructing push notification messages, sending them efficiently to Expo's push notification service, and handling the resulting receipts and errors. The current stable version is 6.1.0. This SDK maintains an active release cadence, with recent major versions (v4, v5, v6) introducing significant breaking changes around module systems and Node.js version support. Key differentiators include its tight integration with the Expo ecosystem, simplifying the complex process of managing push tokens and batching messages, and providing a streamlined API for interacting with the Expo push service. It abstracts away much of the underlying HTTP request handling and error parsing.