Minimalist Approach to send Push Notifications with Expo

const express = require("express");
const { Expo } = require("expo-server-sdk");
const app = express();
const expo = new Expo();
const cors = require("cors");

app.use(cors());
let savedPushTokens = [];
const PORT_NUMBER = 3000;

const handlePushTokens = ({ title, body }) => {
  let notifications = [];
  for (let pushToken of savedPushTokens) {
    if (!Expo.isExpoPushToken(pushToken)) {
      console.error(`Push token ${pushToken} is not a valid Expo push token`);
      continue;
    }

    notifications.push({
      to: pushToken,
      sound: "default",
      title: title,
      body: body,
      data: { body }
    });
  }

  let chunks = expo.chunkPushNotifications(notifications);

  (async () => {
    for (let chunk of chunks) {
      try {
        let receipts = await expo.sendPushNotificationsAsync(chunk);
        console.log(receipts);
      } catch (error) {
        console.error(error);
      }
    }
  })();
};

const saveToken = token => {
  console.log(token, savedPushTokens);
  const exists = savedPushTokens.find(t => t === token);
  if (!exists) {
    savedPushTokens.push(token);
  }
};

app.use(express.json());

app.get("/", (req, res) => {
  res.send("Push Notification Server Running");
});

app.post("/token", (req, res) => {
  saveToken(req.body.token.value);
  console.log(`Received push token, ${req.body.token.value}`);
  res.send(`Received push token, ${req.body.token.value}`);
});

app.post("/message", (req, res) => {
  handlePushTokens(req.body);
  console.log(`Received message, with title: ${req.body.title}`);
  res.send(`Received message, with title: ${req.body.title}`);
});

app.listen(PORT_NUMBER, () => {
  console.log(`Server Online on Port ${PORT_NUMBER}`);
});

//registerForPushNotifications.js
import { Notifications } from 'expo';
import * as Permissions from 'expo-permissions';

const PUSH_ENDPOINT = 'https://easy-soup.glitch.me/token';

const registerForPushNotifications = async () => {
  const { status } = await Permissions.askAsync(Permissions.NOTIFICATIONS);
  if (status !== 'granted') {
    alert('No notification permissions!');
    return;
  }

  // Get the token that identifies this device
  let 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: 'application/json',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      token: {
        value: token,
      }
    }),
  });
}
export default registerForPushNotifications;

//App.js
import React, {useEffect} from 'react';
import { StyleSheet, Text, View } from 'react-native';
import registerForPushNotifications from './registerForPushNotifications';


const App = () => {
  useEffect(() => {
    registerForPushNotifications()
  }, []);
  return (
    <View style={styles.container}>
      <Text>Notifications Example</Text>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});

export default App;