// load geojson data with default variables shown
var mapLayer = L.geoJSON(data[0]['features'], {
    pointToLayer: function (feature, latlng) {
        var marker = L.marker(latlng, {icon: defaultMarker});
        return marker;
    },
    onEachFeature: onEachFeature
}).addTo(map);

// on each marker, do the following
function onEachFeature(feature,layer) {
    layer.bindTooltip(feature.properties.label);
    layer.on('mouseover', function(e){
        layer.setIcon(highlightMarker);
        layer.openTooltip();
    });
    layer.on('mouseout', function(e){
        console.log("mouseout");
        layer.setIcon(defaultMarker);
        layer.closeTooltip();
    });
}