如何扩展 OpenLayers 层非模块化方法？

如何解决如何扩展 OpenLayers 层非模块化方法？

我需要扩展 OpenLayers 层类。由于特定于我的项目的原因，我不能在我的编码中使用模块方法；即我不能使用导入语句。因此，我尝试派生类 Layer 类如下：

    class Graticule extends ol.layer.Layer {

        constructor(viewer,raMin,raMax,decMin,decMax) {
            super({className: "graticule"});

            this.raMin = raMin;
            this.raMax = raMax;
            this.decMin = decMin;
            this.decMax = decMax;

            this.svg = d3
                .select(`#${viewer.getDivId()}`)
                .append('svg')
                .style('position','absolute');
        }

        getSourceState() {
            return ol.source.State.READY;
        }

        render (frameState) {
            var width = frameState.size[0];
            var height = frameState.size[1];
            var projection = frameState.viewState.projection;
            var d3Projection = d3.geoGnomonic().scale(1).translate([0,0]);
            var d3Path = d3.geoPath().projection(d3Projection);

            var pixelBoundsWidth = width;
            var pixelBoundsHeight = height;

            var geoBoundsLeftBottom = [this.raMin,this.decMin];
            var geoBoundsRightTop = [this.raMax,this.decMax];
            var geoBoundsWidth = geoBoundsRightTop[0] - geoBoundsLeftBottom[0];
            if (geoBoundsWidth < 0) {
                geoBoundsWidth += getWidth(projection.getExtent());
            }
            var geoBoundsHeight = geoBoundsRightTop[1] - geoBoundsLeftBottom[1];

            var widthResolution = geoBoundsWidth / pixelBoundsWidth;
            var heightResolution = geoBoundsHeight / pixelBoundsHeight;
            var r = Math.max(widthResolution,heightResolution);
            var scale = r / frameState.viewState.resolution;

            var center = toLonLat(getCenter(frameState.extent),projection);
            d3Projection
                .scale(scale)
                .center(center)
                .translate([width / 2,height / 2]);

            d3Path = d3Path.projection(d3Projection);
            this.svg.attr('width',width);
            this.svg.attr('height',height);

            this.svg.select('path').attr('d',d3Path);

            const graticule = d3.geoGraticule();
            svg.append("graticule").datum(graticule).attr("class","graticule").attr("d",d3Path);

            return this.svg.node();
        }
    }

问题是当我实例化 Graticule 时：

        var graticule = new Graticule(viewer,ramin,ramax,decmin,decmax);

我收到消息错误

Uncaught TypeError: class heritage ol.layer.VectorLayer is not an object or null
    <anonymous> http://localhost:3022/javascript/olqv_graticules.js:1
olqv_graticules.js:1:1
    <anonyme> http://localhost:3022/javascript/olqv_graticules.js:1

任何想法或反应将不胜感激。