push-token.js

import { Notifications, Permissions } from "expo";

const PUSH_ENDPOINT = "https://your-push-server/push-token"

async function registerForPushNotificationsAsync() {
  // Request permissions -- same as earlier
  [...]
  
  // Get the token that uniquely identifies this device
  const token = await Notifications.getExpoPushTokenAsync();

  // POST the token to your backend server from where you can retrieve it to send push notifications.
  return fetch(PUSH_ENDPOINT, {
    method: "POST",
    headers: {
      Accept: "Content-Type": "application/json",
    },
    body: JSON.stringify({
      token: {
        value: token,
      },
      user: {
        userId: "current_user_id",
      },
    }),
  });
 }