index.js attempt to read db

$(document).ready(function () {
  let PIXELSIZE = 2;
  let REPEATSX = 20;
  let REPEATSY = 15;
  let DIMENSION = 25;

  let canvas = id('mycanvas');
  let ctx = canvas.getContext("2d");
  let canvasWidth = DIMENSION * REPEATSX * PIXELSIZE;
  let canvasHeight = DIMENSION * REPEATSY * PIXELSIZE;
  let selectedBox = null;

  canvas.width = canvasWidth;
  canvas.height = canvasHeight;

  // Your web app's Firebase configuration
  var firebaseConfig = {
    apiKey: "AIzaSyDjLFcsO92KpwLiFe7Hsp4gVd51w61WIsk",
    authDomain: "canvasgamedemo.firebaseapp.com",
    databaseURL: "https://canvasgamedemo.firebaseio.com",
    projectId: "canvasgamedemo",
    storageBucket: "canvasgamedemo.appspot.com",
    messagingSenderId: "258751262925",
    appId: "1:258751262925:web:50cdf23c2265aa7ae07984"
  };
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);
  let db = firebase.firestore();

  db.collection('app').onSnapshot(function (grid) {
    console.log(grid);
    for(let change of grid.docChanges()) {
      console.log(change);
      if (!change.doc) continue;
      let key = change.doc.id;
      let data = change.doc.data().data;
      if (key == 'grid') continue;
    }
  });
// ...