JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://openlayers.org/dev/theme/default/style.css">
<script src="http://openlayers.org/dev/OpenLayers.js"></script>
<div id="map" class="smallmap"></div>

CSS

#map{
    width:450px;
    height:400px;
}

            /* avoid pink tiles */
            .olImageLoadError {
                background-color: transparent !important;
            }

JavaScript

var map = new OpenLayers.Map('map');

var wmsLayer = new OpenLayers.Layer.WMS( "OpenLayers WMS",
	"http://vmap0.tiles.osgeo.org/wms/vmap0?", {layers: 'basic'});

var polygonLayer = new OpenLayers.Layer.Vector("Polygon Layer");

map.addLayers([wmsLayer,polygonLayer]);
map.addControl(new OpenLayers.Control.LayerSwitcher());
map.addControl(new OpenLayers.Control.MousePosition());

var  polygon= new OpenLayers.Control.DrawFeature(polygonLayer,OpenLayers.Handler.Polygon);

map.addControl(polygon);


map.setCenter(new OpenLayers.LonLat(51.020848706522152, 5.2810711885084611), 3);

//activate the control
polygon.activate();

polygonLayer.events.register('featureadded',polygonLayer, onAdded);


function onAdded(ev){
	var polygon=ev.feature.geometry;
	var bounds=polygon.getBounds();
	//now do whatever you want with the bounds
	//I'm just alerting it				
	alert(bounds);
}