Dynamically update html page text base don the d3 tree node selected

I have a working D3 collapsible tree based on this example. I have added a paragraph element at the top of my html page (in a separate div) that I want to update the text of based on the tree node a user clicks. Using the example linked above, if a user clicks on the "analytics" node the tree should expand to show children of "analytics" and the paragraph text at the top of my page should update to "analytics". My tree is working fine but I am not able to figure out how to update the paragraph text.

I am able to update this paragraph text to a fixed value but not based on the node clicked.

So this works:

d3.select("p").text("This is paragraph.")

but this does not:

d3.select("p").text(function (d) {
  return d.name;
})

Can you help with this? Thanks.

To update p text you can attach on click handler to the node:

nodeEnter.on("click", (event, d) => {
    d.children = d.children ? null : d._children;
    update(d);
    d3.select("#node-info").text(d.data.name);
  });

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

    const data = {
      "name": "flare",
      "children": [
        {
          "name": "analytics",
          "children": [
            {
              "name": "cluster",
              "children": [
                {"name": "AgglomerativeCluster", "value": 3938},
                {"name": "CommunityStructure", "value": 3812},
                {"name": "HierarchicalCluster", "value": 6714},
                {"name": "MergeEdge", "value": 743}
              ]
            },
            {
              "name": "graph",
              "children": [
                {"name": "BetweennessCentrality", "value": 3534},
                {"name": "LinkDistance", "value": 5731},
                {"name": "MaxFlowMinCut", "value": 7840},
                {"name": "ShortestPaths", "value": 5914},
                {"name": "SpanningTree", "value": 3416}
              ]
            },
            {
              "name": "optimization",
              "children": [
                {"name": "AspectRatioBanker", "value": 7074}
              ]
            }
          ]
        }
      ]
    };

    const width = 954;
    const dx = 10;
    const dy = width / 6;
    const margin = {top: 10, right: 120, bottom: 10, left: 40};

    const diagonal = d3.linkHorizontal().x(d => d.y).y(d => d.x);
    const tree = d3.tree().nodeSize([dx, dy]);

    const root = d3.hierarchy(data);

    root.x0 = dy / 2;
    root.y0 = 0;
    root.descendants().forEach((d, i) => {
      d.id = i;
      d._children = d.children;
      if (d.depth && d.data.name.length !== 7) d.children = null;
    });

    const svg = d3.create("svg")
      .attr("viewBox", [-margin.left, -margin.top, width, dx])
      .style("font", "10px sans-serif")
      .style("user-select", "none");

    const gLink = svg.append("g")
      .attr("fill", "none")
      .attr("stroke", "#555")
      .attr("stroke-opacity", 0.4)
      .attr("stroke-width", 1.5);

    const gNode = svg.append("g")
      .attr("cursor", "pointer")
      .attr("pointer-events", "all");

    function update(source) {
      const duration = d3.event && d3.event.altKey ? 2500 : 250;
      const nodes = root.descendants().reverse();
      const links = root.links();

      tree(root);

      let left = root;
      let right = root;
      root.eachBefore(node => {
        if (node.x < left.x) left = node;
        if (node.x > right.x) right = node;
      });

      const height = right.x - left.x + margin.top + margin.bottom;

  const transition = svg.transition()
      .duration(duration)
      .attr("viewBox", [-margin.left, left.x - margin.top, width, height])
      .tween("resize", window.ResizeObserver ? null : () => () => svg.dispatch("toggle"));

  const node = gNode.selectAll("g")
    .data(nodes, d => d.id);

  const nodeEnter = node.enter().append("g")
      .attr("transform", d => `translate(${source.y0},${source.x0})`)
      .attr("fill-opacity", 0)
      .attr("stroke-opacity", 0)
      .on("click", (event, d) => {
        d.children = d.children ? null : d._children;
        update(d);
      });

 nodeEnter.on("click", (event, d) => {
  d.children = d.children ? null : d._children;
  update(d);
  d3.select("#node-info").text(d.data.name);
});
      
  nodeEnter.append("circle")
      .attr("r", 2.5)
      .attr("fill", d => d._children ? "#555" : "#999")
      .attr("stroke-width", 10);

  nodeEnter.append("text")
      .attr("dy", "0.31em")
      .attr("x", d => d._children ? -6 : 6)
      .attr("text-anchor", d => d._children ? "end" : "start")
      .text(d => d.data.name)
    .clone(true).lower()
      .attr("stroke-linejoin", "round")
      .attr("stroke-width", 3)
      .attr("stroke", "white");

  const nodeUpdate = node.merge(nodeEnter).transition(transition)
      .attr("transform", d => `translate(${d.y},${d.x})`)
      .attr("fill-opacity", 1)
      .attr("stroke-opacity", 1);

  const nodeExit = node.exit().transition(transition).remove()
      .attr("transform", d => `translate(${source.y},${source.x})`)
      .attr("fill-opacity", 0)
      .attr("stroke-opacity", 0);

  const link = gLink.selectAll("path")
    .data(links, d => d.target.id);

  const linkEnter = link.enter().append("path")
      .attr("d", d => {
        const o = {x: source.x0, y: source.y0};
        return diagonal({source: o, target: o});
      });

  link.merge(linkEnter).transition(transition)
      .attr("d", diagonal);

  link.exit().transition(transition).remove()
      .attr("d", d => {
        const o = {x: source.x, y: source.y};
        return diagonal({source: o, target: o});
      });

  root.eachBefore(d => {
    d.x0 = d.x;
    d.y0 = d.y;
  });
}

update(root);

document.body.appendChild(svg.node());

<!-- language: lang-css -->

.text{
  min-height:70px;
}

<!-- language: lang-html -->

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/7.8.4/d3.min.js"></script>
<div class="text">
 <p>Clicked node text:</p>
 <p id="node-info"></p>
</div>

<!-- end snippet -->