Split Polygon by Line

polygon_split.js

onGeomChange = (e) => {
      /*
          This function will dynamically split the polygon into two parts by a line and will follow geometry change event.
      */

      //Create jsts parser to read openlayers geometry
      let parser = new jsts.io.OL3Parser();

      //Creating line geometry from draw intraction
      let linestring = new ol.Feature({    
          geometry: new ol.geom.LineString(e.target.getCoordinates())
      });        

      //Parse Polygon and Line geomtry to jsts type
      let a = parser.read(polygon.getGeometry())
      let b = parser.read(linestring.getGeometry())               

      //Perform union of Polygon and Line and use Polygonizer to split the polygon by line
      let union = a.getExteriorRing().union(b);
      let polygonizer = new jsts.operation.polygonize.Polygonizer();

      //Splitting polygon in two part
      polygonizer.add(union);

      //Get splitted polygons
      let polygons = polygonizer.getPolygons();

      //This will execute only if polygon is successfully splitted into two parts
      if(polygons.array.length == 2) {            

          //Clear old splitted polygons and measurement overlays
          this.vector_layer.getSource().clear();
          this.map.getOverlays().clear();              

          //Iterate through splitted polygons
          polygons.array.forEach((geom) => {                                                
              let splitted_polygon = new ol.Feature({    
                  geometry: new ol.geom.Polygon(parser.write(geom).getCoordinates())
              });                

              //Add splitted polygon to vector layer    
              this.vector_layer.getSource().addFeature(splitted_polygon);

              //Add area measurement overlay to splitted polygon
              let overlay = new Overlay(this.map).overlay;
              this.calArea(overlay, splitted_polygon.getGeometry().getFlatInteriorPoint(), splitted_polygon.getGeometry().getArea());

              //Add line measurement overlay to segment of polygon
              let polyCoords = splitted_polygon.getGeometry().getCoordinates()[0];
              polyCoords.forEach((coords, i) => {    
                  if(i < polyCoords.length-1){                        
                      let line = new ol.geom.LineString([coords, polyCoords[i+1]]);                        
                      let overlay = new Overlay(this.map).overlay;
                      this.calDistance(overlay, line.getFlatMidpoint(), line.getLength());    
                  }
              });
          });

          //Change Style of Splitted polygons
          this.vector_layer.setStyle(highlightStyle);
      }
      else {
          //Change style to normal if polgon is not splitted            
          this.vector_layer.setStyle(regularStyle);

          //Clear measurement overlays and splitted polygon if line is not completely intersected with polygon
          this.map.getOverlays().clear();
          this.vector_layer.getSource().clear();

          //Add original polygon to vector layer if no intersection is there between line and polygon
          this.vector_layer.getSource().addFeature(polygon)
      }
        
}