PolygonsMerge.js

let mergePolygon = (e) => {
    /*
        This function is applicable to merge only two polygons
        This function will merge or perform union on two adjacent polygons. For the merge function to work, the polygons should atleast intersect each other.
    */
    
    //Create jsts parser to read openlayers geometry
    let parser = new jsts.io.OL3Parser();       
    
    //Parse Polygons geometry to jsts type
    let a = parser.read(vector_layer.getSource().getFeatures()[0].getGeometry());
    let b = parser.read(vector_layer.getSource().getFeatures()[1].getGeometry());
    
    //Perform union of Polygons. The union function below will merge two polygon together
    let union = a.union(b);    
    let merged_polygon = new ol.Feature({    
        geometry: new ol.geom.Polygon(parser.write(union).getCoordinates())
    });     
    vector_layer.getSource().clear();
    vector_layer.getSource().addFeature(merged_polygon);
    vector_layer.setStyle(highlightStyle);
};