当拖动一个节点时，链接应使用新坐标更新。当前代码不清除旧路径。我使用了join方法，但是group元素没有清理附加的子元素。

svg_arc()

function svg_arc() {
        var svg = d3.select('body')
                .append('svg')
                .attr('width',410)
                .attr('height',500)
                //.style('border','10px solid red')
                .style('background','#ececec')
        
        var g = svg.append('g')
                .attr('stroke','black')
                .attr('stroke-width',1)
                .attr('fill','black')       
        
        var data = [
                {
                        id:"pointA",
                        x:100,
                        y:350,
                        r:6,
                        text:'A'
                },{
                        id:"pointB",
                        x:250,
                        y:50,
                        r:6,
                        text:'B'
                },{
                        id:"pointC",
                        x:400,
                        y:350,
                        r:6,
                        text:'C'
                }
        ]
        var node = g.selectAll('.node')
                .data(data)
                .join('g')
                .attr('class','node')
                .attr('transform',d => `translate(${d.x},${d.y})`)
                .attr("pointer-events", "all")
        
        var circle = node.append('circle')
                .attr('id',d => d.id)
                .attr('cx',0)
                .attr('cy',0)
                .attr('r',d => d.r)
                .attr("pointer-events", "all")

        var text = node.append('text')
                .attr('class','text')
                .text(d => d.text)
                .attr('x',0)
                .attr('y',0)
                .attr('dx',-15)
                .attr('dy',-15)

        node.call(
                d3.drag()
                        .on("start",function(event,d) {
                                d3.select(this).raise().classed("active", true);
                        })                          
                        .on("drag",function(event,d) {
                                
                                d.x += event.dx
                                d.y += event.dy
                                update_links(g,data)
                                d3.select(this).attr('transform',`translate(${d.x},${d.y})`)
                        })
                        .on("end", function dragEnd(event,d) {
                                d3.select(this).classed("active", false);
                        })
        )

        update_links(g,data)
}

function update_links(g,n) {
        var data = [0]//dummy data
        var line = g.selectAll('.lines')
                .data(data)
                .join('g')
                .attr('class','lines')
        
        line.append('path')
                .attr('class','AB')
                .attr('d',['M',n[0].x,n[0].y,'L',n[1].x,n[1].y].join(' '))
                .attr('stroke','black')

        line.append('path')
                .attr('class','BC')
                .attr('d',['M',n[1].x,n[1].y,'L',n[2].x,n[2].y].join(' '))
                .attr('stroke','black')

        line.append('path')
                .attr('class','AC')     
                .attr('d',['M',n[0].x,n[0].y,'Q',n[1].x,n[1].y,n[2].x,n[2].y].join(' '))
                .attr('stroke','black')
                .attr('fill','none')

        line.append('path')
                .attr('class','MID')
                .attr('d',['M',(n[0].x+n[1].x)/2,(n[0].y+n[1].y)/2,'L',(n[1].x+n[2].x)/2,(n[1].y+n[2].y)/2].join(' '))
                .attr('fill','none')
        
}

<script src="https://unpkg.com/d3@7.0.4/dist/d3.min.js"></script>