Google Map with multiple markers - Geocoded addresses, unique InfoWindows, and automatic zoom and centering to show all markers. Working demo here: https://codepen.io/bootsified/details/XWbgwNr

google_map_multiple_markers_geocoding.html

<!--
* GOOGLE MAP W/ MULTIPLE MARKERS AND OPTIONAL GEOCODING
* by Boots (www.boots.media)
* Working demo here: https://codepen.io/bootsified/details/XWbgwNr
* 
* To use geocoding for locations, set `useGeocoding = true;` (limit 10 locations).
* To manually place markers by lat/lng, set `useGeocoding = false;` (no limit). Locations array must contain lat/lng data.
-->

<script src="https://maps.googleapis.com/maps/api/js?key=[YOUR_APP_KEY_GOES_HERE]"></script>
<script>
	// Set global variables
	var map;
	var bounds;
	var locationCount;
	var mapOptions;
	var infoWindow = null;
	var defaultZoom = 14; // The minimum zoom level
	var mapElementId = "myGoogleMap";
	var mapElement = document.getElementById(mapElementId);
	var useGeocoding = true; // true: geocode marker from street address, false: set markers using lat/lng

	// Set marker attributes. If you need unique values for each marker,
	// you can update the values directly in the locations array.
	var markerWidth = 32;
	var markerHeight = 32;
	var markerScale = 1; // Scale the image, if you can't control the source file (0 - 1).

	// The array of locations to mark on the map.
	// Google limits geocoded locations to 10 per pageload.
	// No limit for markers set with lat/lng.
	var locations = [
		[
			"Empire State Building", // name
			"20 W 34th St", // street
			"", // street 2 (ex. Suite 1234)
			"New York", // city
			"NY", // state
			"10001", // zip
			{
				// Marker icon config object
				url: "https://maps.google.com/mapfiles/ms/micons/blue.png",
				size: new google.maps.Size(markerWidth, markerHeight),
				origin: new google.maps.Point(0, 0),
				anchor: new google.maps.Point(markerWidth * (markerScale / 2), markerHeight * markerScale),
				scaledSize: new google.maps.Size(markerWidth * markerScale, markerHeight * markerScale)
			},
			new google.maps.Size(markerWidth * (markerScale / 4) * -1, markerHeight * markerScale), // marker offset
			new google.maps.LatLng(40.7484995, -73.9882267)
		],
		[
			"Independence Hall", // name
			"520 Chestnut St", // street
			"", // street 2 (ex. Suite 1234)
			"Philadelphia", // city
			"PA", // state
			"19106", // zip
			{
				// Marker icon config object
				url: "https://maps.google.com/mapfiles/ms/micons/red.png",
				size: new google.maps.Size(markerWidth, markerHeight),
				origin: new google.maps.Point(0, 0),
				anchor: new google.maps.Point(markerWidth * (markerScale / 2), markerHeight * markerScale),
				scaledSize: new google.maps.Size(markerWidth * markerScale, markerHeight * markerScale)
			},
			new google.maps.Size(markerWidth * (markerScale / 4) * -1, markerHeight * markerScale), // marker offset
			new google.maps.LatLng(39.949140, -75.149730)
		]
	];

	// Init map on Google 'load' event
	google.maps.event.addDomListener(window, "load", init);

	// Init the map
	function init() {
		// Customize look of the map.
		// https://www.mapbuildr.com/
		mapOptions = {
			zoom: defaultZoom,
			zoomControl: true,
			zoomControlOptions: {
				style: google.maps.ZoomControlStyle.SMALL
			},
			disableDoubleClickZoom: false,
			mapTypeControl: false,
			panControl: false,
			scaleControl: false,
			scrollwheel: false,
			streetViewControl: false,
			draggable: true,
			overviewMapControl: false,
			mapTypeId: google.maps.MapTypeId.ROADMAP,
			styles: [
				{
					featureType: "all",
					stylers: [{ saturation: -100 }, { gamma: 0.8 }]
				},
				{
					featureType: "poi",
					stylers: [{ visibility: "off" }]
				},
				{
					featureType: "transit",
					stylers: [{ visibility: "off" }]
				}
			]
		};

		// Create new map object
		map = new google.maps.Map(mapElement, mapOptions);

		// OPTIONAL: Set listener to tell when map is idle
		// Can be useful during dev
		// google.maps.event.addListener(map, "idle", function() {
			// console.log("map is idle");
		// });
		
		if (useGeocoding) {
			var geocoder = new google.maps.Geocoder();
		}
		bounds = new google.maps.LatLngBounds();
		locationCount = 0;

		// Init InfoWindow and leave it
		// for use when user clicks marker
		infoWindow = new google.maps.InfoWindow({ content: "Loading content..." });

		// Loop through locations and set markers
		for (i = 0; i < locations.length; i++) {
			if (useGeocoding) {
				// street+city,state+zip
				var address = locations[i][1] + "+" + locations[i][2] + "," + locations[i][3] + "+" + locations[i][4];

				//Get latitude and longitude from address
				geocoder.geocode({ address: address }, onGeocodeComplete(i));
			} else {
				placeLatLngMarker(i);
			}
		}

		// Re-center map on window resize
		google.maps.event.addDomListener(window, "resize", function() {
			var center = map.getCenter();
			google.maps.event.trigger(map, "resize");
			map.setCenter(center);
		});
	} // END init()

	// Triggered as the geocode callback
	function onGeocodeComplete(i) {
		// Callback function for geocode on response from Google.
		// We wrap it in 'onGeocodeComplete' so we can send the
		// location index through to the marker to establish
		// content.
		var geocodeCallBack = function(results, status) {
			if (status == google.maps.GeocoderStatus.OK) {
				// Create the marker for the location
				// We use 'html' key to attach the
				// InfoWindow content to the marker.
				var marker = new google.maps.Marker({
					icon: locations[i][6],
					position: results[0].geometry.location,
					map: map,
					window_offset: locations[i][7],
					html: getInfoWindowContent(i)
				});

				// Set event to display the InfoWindow anchored
				// to the marker when the marker is clicked.
				google.maps.event.addListener(marker, "click", function() {
					showInfoWindow(this);
				});

				// Add this marker to the map bounds
				extendBounds(results[0].geometry.location);
			} else {
				console.log("Location geocoding has failed: " + google.maps.GeocoderStatus);

				// Hide empty map element on error
				mapElement.style.display = "none";
			}
		}; // END geocodeCallBack()

		return geocodeCallBack;
	} // END onGeocodeComplete()

	function placeLatLngMarker(i) {
		// Create the marker for the location
		// We use 'html' key to attach the
		// InfoWindow content to the marker.
		var marker = new google.maps.Marker({
			icon: locations[i][6],
			position: locations[i][8],
			map: map,
			window_offset: locations[i][7],
			html: getInfoWindowContent(i)
		});

		// Set event to display the InfoWindow anchored
		// to the marker when the marker is clicked.
		google.maps.event.addListener(marker, "click", function() {
			showInfoWindow(this);
		});

		// Add this marker to the map bounds
		extendBounds(locations[i][8]);
	}

	// The HTML content for the InfoWindow.
	// Includes a form to allow the user to
	// get directions.
	function getInfoWindowContent(i) {
		var windowContent = '<form id="form-directions" action="http://maps.google.com/maps" method="get" target="_blank">\
			<p><strong>' + locations[i][0] + '</strong><br>\
			' + locations[i][1] + ', ' + locations[i][2] + '<br>\
			' + locations[i][3] + ', ' + locations[i][4] + ' ' + locations[i][5] + '</p>\
			<input type="hidden" name="daddr" value="' + locations[i][1] + ', ' + locations[i][3] + ', ' + locations[i][4] + ' ' + locations[i][5] + '" />\
			<label for="saddr" class="alt-italic">Need directions?</label>\
			<div class="input-group input-group--inline input-group--sm">\
			<input name="saddr" type="text" class="input-group__input" placeholder="Your Address...">\
			<button class="input-group__btn button" type="submit">Go!</button>\
			</div><!-- /input-group -->\
			</form>';

		return windowContent;
	}

	function showInfoWindow(marker) {
		// Updates the InfoWindow content with
		// the HTML held in the marker ('this').
		infoWindow.setOptions({
			content: marker.html,
			pixelOffset: marker.window_offset
		});
		infoWindow.open(map, marker);
	}

	// Establishes the bounds for all the markers
	// then centers and zooms the map to show all.
	function extendBounds(latlng) {
		++locationCount;

		bounds.extend(latlng);

		if (locationCount == locations.length) {
			map.fitBounds(bounds);

			var currentZoom = map.getZoom();
			if (currentZoom > mapOptions.zoom) {
				map.setZoom(mapOptions.zoom);
			}
		}
	} // END extendBounds()
</script>

<style>
	.google-map {
		background-color: #e0e0e0;
		height: 40rem;
		max-height: 100vh;
	}
</style>

<div id="myGoogleMap" class="google-map"></div>

@untiedshoes It's actually much simpler to set markers by lat/lng. I've updated the gist with that option, as well as cleaning things up a bit more. You can also now see a working demo here: https://codepen.io/bootsified/details/XWbgwNr.

I never thought about adding that option. Makes total sense. Thanks for the suggestion. 🙌

Awesome man!!
I've literally (in just the last 10 mins), also done my own solution.

Be interesting to see how you've done it too :)