How to use the @hpcc-js/common.extent function in @hpcc-js/common

layerUpdate(map: Map) {
        super.layerUpdate(map);
        this._palette = this._palette.switch(this.paletteID());
        if (this.useClonedPalette()) {
            this._palette = this._palette.cloneNotExists(this.paletteID() + "_" + this.id());
        }

        const latFunc = this.cellFunc(this.latitudeColumn(), 0);
        const longFunc = this.cellFunc(this.longitudeColumn(), 0);
        const latLongFunc = (row): [number, number] => [+latFunc(row), +longFunc(row)];
        const weightFunc = this.cellFunc(this.weightColumn(), 0);

        const data: any[][] = this.data();

        const extent = d3Extent(data, weightFunc);

        const format = this.weightFormat() ? d3Format(this.weightFormat()) : _ => _;

        this.clear();
        data.forEach(row => {
            const circle = new Marker(latLongFunc(row), {
                icon: this.createIcon(weightFunc(row), this._palette(weightFunc(row), extent[0], extent[1]), format),
                origRow: row
            } as any).on("click", e => this.clickHandler(e, row));
            circle.bindTooltip("Weight:  " + weightFunc(row));
            this.add(circle);
        });
    }

updateHexagons() {
        this._palette = this._palette.switch(this.paletteID());
        if (this.useClonedPalette()) {
            this._palette = this._palette.cloneNotExists(this.paletteID() + "_" + this.id());
        }

        const polyFunc = this.cellFunc(this.polygonColumn(), []);
        const weightFunc = this.cellFunc(this.weightColumn(), 0);

        const data = this.data();

        const extent = d3Extent(data, weightFunc);

        this.clear();
        data.forEach(row => {
            this.add(new Polygon(this.fixDateLine(polyFunc(row)).map(lngLat2LatLng), {
                color: this._palette(extent[1], extent[0], extent[1]),
                fillColor: this._palette(weightFunc(row), extent[0], extent[1]),
                fillOpacity: this.opacity(),
                weight: 1,
                origRow: row
            } as any).on("click", e => this.clickHandler(e, row)));
        });
    }