index.js

/**
 * @license
 * Copyright 2019 Google LLC. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */
// [START maps_layer_data_quakes_red]
let map;

function initMap() {
  map = new google.maps.Map(document.getElementById("map"), {
    center: { lat: 20, lng: -160 },
    zoom: 2,
  });

  // Get the earthquake data (JSONP format)
  // This feed is a copy from the USGS feed, you can find the originals here:
  //   http://earthquake.usgs.gov/earthquakes/feed/v1.0/geojson.php
  const script = document.createElement("script");

  script.setAttribute(
    "src",
    "https://storage.googleapis.com/mapsdevsite/json/quakes.geo.json"
  );
  document.getElementsByTagName("head")[0].appendChild(script);
  // Add a basic style.
  map.data.setStyle((feature) => {
    const mag = Math.exp(parseFloat(feature.getProperty("mag"))) * 0.1;
    return /** @type {google.maps.Data.StyleOptions} */ {
      icon: {
        path: google.maps.SymbolPath.CIRCLE,
        scale: mag,
        fillColor: "#f00",
        fillOpacity: 0.35,
        strokeWeight: 0,
      },
    };
  });
}

// Defines the callback function referenced in the jsonp file.
function eqfeed_callback(data) {
  map.data.addGeoJson(data);
}

window.initMap = initMap;
window.eqfeed_callback = eqfeed_callback;
// [END maps_layer_data_quakes_red]