I am trying to add multiple markers each with its own infowindow that comes up when clicked on. I am having trouble with getting the infowindows coming up, when I try it either shows up only one marker without an infowindow.

Thanks, let me know if you need some more information

<meta name="viewport" content="initial-scale=1.0, user-scalable=no"/>
<style type="text/css">
html {
    height: 100%
}

body {
    height: 100%;
    margin: 0;
    padding: 0
}

#map_canvas {
    height: 100%
}
</style>
<script type="text/javascript"
    src="http://maps.googleapis.com/maps/api/js?key=AIzaSyB1tbIAqN0XqcgTR1-FxYoVTVq6Is6lD98&sensor=false">
</script>
<script type="text/javascript">

var locations = [
    ['loan 1', 33.890542, 151.274856, 'address 1'],
    ['loan 2', 33.923036, 151.259052, 'address 2'],
    ['loan 3', 34.028249, 151.157507, 'address 3'],
    ['loan 4', 33.80010128657071, 151.28747820854187, 'address 4'],
    ['loan 5', 33.950198, 151.259302, 'address 5']
];

function initialize() {

    var myOptions = {
        center: new google.maps.LatLng(33.890542, 151.274856),
        zoom: 8,
        mapTypeId: google.maps.MapTypeId.ROADMAP

    };
    var map = new google.maps.Map(document.getElementById("default"),
        myOptions);

    setMarkers(map, locations)
}


function setMarkers(map, locations) {

    var marker, i
    for (i = 0; i < locations.length; i++) {

        var loan = locations[i][0]
        var lat = locations[i][1]
        var long = locations[i][2]
        var add = locations[i][3]

        latlngset = new google.maps.LatLng(lat, long);

        var marker = new google.maps.Marker({
            map: map, title: loan, position: latlngset
        });
        map.setCenter(marker.getPosition())

        var content = "Loan Number: " + loan + '</h3>' + "Address: " + add

        var infowindow = new google.maps.InfoWindow()

        google.maps.AddListener(marker, 'click', function (map, marker) {
            infowindow.setContent(content)
            infowindow.open(map, marker)
        });
    }
}


</script>
</head>
<body onload="initialize()">
<div id="default" style="width:100%; height:100%"></div>
</body>
</html>

You could use a closure. Just modify your code like this:

google.maps.event.addListener(marker,'click', (function(marker,content,infowindow){ 
    return function() {
        infowindow.setContent(content);
        infowindow.open(map,marker);
    };
})(marker,content,infowindow));  

Here is the DEMO


Here is the code snippet which will work for sure. You can visit below link for working jsFiddle and explainantion in detail. How to locate multiple addresses on google maps with perfect zoom

var infowindow = new google.maps.InfoWindow();  
google.maps.event.addListener(marker, 'mouseover', (function(marker) {  
           return function() {  
               var content = address;  
               infowindow.setContent(content);  
               infowindow.open(map, marker);  
           }  
         })(marker));  

Source Link

Demo Link

The following code will show Multiple Markers with InfoWindow. You can Uncomment code to show Info on Hover as well

enter image description here

            var map;
            var InforObj = [];
            var centerCords = {
                lat: -25.344,
                lng: 131.036
            };
            var markersOnMap = [{
                    placeName: "Australia (Uluru)",
                    LatLng: [{
                        lat: -25.344,
                        lng: 131.036
                    }]
                },
                {
                    placeName: "Australia (Melbourne)",
                    LatLng: [{
                        lat: -37.852086,
                        lng: 504.985963
                    }]
                },
                {
                    placeName: "Australia (Canberra)",
                    LatLng: [{
                        lat: -35.299085,
                        lng: 509.109615
                    }]
                },
                {
                    placeName: "Australia (Gold Coast)",
                    LatLng: [{
                        lat: -28.013044,
                        lng: 513.425586
                    }]
                },
                {
                    placeName: "Australia (Perth)",
                    LatLng: [{
                        lat: -31.951994,
                        lng: 475.858081
                    }]
                }
            ];

            window.onload = function () {
                initMap();
            };

            function addMarkerInfo() {
                for (var i = 0; i < markersOnMap.length; i++) {
                    var contentString = '<div id="content"><h1>' + markersOnMap[i].placeName +
                        '</h1><p>Lorem ipsum dolor sit amet, vix mutat posse suscipit id, vel ea tantas omittam detraxit.</p></div>';

                    const marker = new google.maps.Marker({
                        position: markersOnMap[i].LatLng[0],
                        map: map
                    });

                    const infowindow = new google.maps.InfoWindow({
                        content: contentString,
                        maxWidth: 200
                    });

                    marker.addListener('click', function () {
                        closeOtherInfo();
                        infowindow.open(marker.get('map'), marker);
                        InforObj[0] = infowindow;
                    });
                    // marker.addListener('mouseover', function () {
                    //     closeOtherInfo();
                    //     infowindow.open(marker.get('map'), marker);
                    //     InforObj[0] = infowindow;
                    // });
                    // marker.addListener('mouseout', function () {
                    //     closeOtherInfo();
                    //     infowindow.close();
                    //     InforObj[0] = infowindow;
                    // });
                }
            }

            function closeOtherInfo() {
                if (InforObj.length > 0) {
                    InforObj[0].set("marker", null);
                    InforObj[0].close();
                    InforObj.length = 0;
                }
            }

            function initMap() {
                map = new google.maps.Map(document.getElementById('map'), {
                    zoom: 4,
                    center: centerCords
                });
                addMarkerInfo();
            }

If you also want to bind closing of infowindow to some event, try something like this

google.maps.event.addListener(marker,'click', (function(marker,content,infowindow){ 
    return function() {
        infowindow.setContent(content);
        infowindow.open(map,marker);
        windows.push(infowindow)
        google.maps.event.addListener(map,'click', function(){ 
            infowindow.close();
        }); 
    };
})(marker,content,infowindow));