Drag functions for simulation

dragFunctions.js

drag = (simulation) => {
        function dragstarted(event, d) {
            d.fx = event.x;
            d.fy = event.y;
            simulation.alphaTarget(0.3).restart();
        }
        function dragged(event, d) {
            d.fx = event.x;
            d.fy = event.y;
        }
        function dragended(event, d) {
            d.fx = null;
            d.fy = null;
            simulation.alphaTarget(0);
        }
        return d3.drag()
            .on("start", dragstarted)
            .on("drag", dragged)
            .on("end", dragended);
    }