openlayers 5 bbox

function drawbbox() {
    var bbox = map.getView().calculateExtent();
    var coord = [[
        [bbox[0], bbox[1]],
        [bbox[0], bbox[3]],
        [bbox[2], bbox[3]],
        [bbox[2], bbox[1]],
        [bbox[0], bbox[1]]
    ]];

    var geojsonObject = {
        'type': 'FeatureCollection',
        'crs': {
            'type': 'name',
            'properties': {
                'name': 'EPSG:3857'
            }
        },
        'features': [{
            'type': 'Feature',
            'geometry': {
                'type': 'Polygon',
                'coordinates': coord
            }
        }]
    };

    var bboxSource = new ol.source.Vector({
        features: new ol.format.GeoJSON().readFeatures(geojsonObject)
    });

    var bbox = new ol.layer.Vector({
        name: 'Select',
        source: bboxSource,
        style: new ol.style.Style({
            stroke: new ol.style.Stroke({
                color: 'blue'
            }),
            fill: new ol.style.Fill({
                color: [0, 0, 255, 0.05]
            })
        })
    });
    map.addLayer(bbox);
}