How to use the geojs.inherit function in geojs

/* The geometry can be specified using 0-point coordinates and deltas
                         * since it is a regular grid. */
                        x0: data.x0, y0: data.y0, dx: data.dx, dy: data.dy
                    });
            }

            if (done) {
                done(contour);
            }
        }

        that._readObject(file, _done, progress);
    };
};

geo.inherit(geo.contourJsonReader, geo.fileReader);

geo.registerFileReader('contourJsonReader', geo.contourJsonReader);