Style the previous links to a child on hover in D3 - d3.js

Question

I'm working on a tree chart in D3.js.
I try to modify the color of the previous links (on the picture = the blue lines) when I put my mouse on a child rectangle (on the picture = the red dot).
Is there a way to access to the path of links when hover event on the rectangle is triggered please?

Answer 1

Below, you can see a d3 v6 version of the v3 example in the other question.
The v6 example is taken from this block but with the 'path tracing' added back in. I've changed the 'path tracing' from the click to the mouseover event so you see the effect whilst hovering over a node.
A few changes worth noting:
For links d.source.id and d.target.id become d.parent.id and d.id respectively.
treeData source data definition is just an object not an array with a single object
nodes and links are created with a different method but the enter/ update/ exit logic is very similar (bar the source / parent comment above for the links)
var treeData = {
"name": "Top Level",
"parent": "null",
"children": [{
"name": "Level 2: A",
"parent": "Top Level",
"children": [{
"name": "Son of A",
"parent": "Level 2: A"
}, {
"name": "Daughter of A",
"parent": "Level 2: A"
}]
}, {
"name": "Level 2: B",
"parent": "Top Level"
}]
};
// ************** Generate the tree diagram *****************
// Set the dimensions and margins of the diagram
var margin = {top: 20, right: 90, bottom: 30, left: 90},
width = 960 - margin.left - margin.right,
height = 180 - margin.top - margin.bottom;
// append the svg object to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
var svg = d3.select("body").append("svg")
.attr("width", width + margin.right + margin.left)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate("
+ margin.left + "," + margin.top + ")");
var i = 0,
duration = 750,
root;
// declares a tree layout and assigns the size
var treemap = d3.tree().size([height, width]);
// Assigns parent, children, height, depth
root = d3.hierarchy(treeData, function(d) { return d.children; });
root.x0 = height / 2;
root.y0 = 0;
update(root);
function update(source) {
// Assigns the x and y position for the nodes
var treeData = treemap(root);
// Compute the new tree layout.
var nodes = treeData.descendants(),
links = treeData.descendants().slice(1);
// Normalize for fixed-depth.
nodes.forEach(function(d) {
d.y = d.depth * 180;
});
// Update the nodes…
var node = svg.selectAll('g.node')
.data(nodes, function(d) {return d.id || (d.id = ++i); });
// Enter any new modes at the parent's previous position.
var nodeEnter = node.enter().append('g')
.attr('class', 'node')
.attr("transform", function(d) {
return "translate(" + source.y0 + "," + source.x0 + ")";
})
.on('mouseover', mouseover);
// Add Circle for the nodes
nodeEnter.append('circle')
.attr('class', 'node')
.attr("id", function(d){return "node" + d.id;})
.attr('r', 1e-6)
.style("fill", function(d) {
return d._children ? "lightsteelblue" : "#fff";
});
// Add labels for the nodes
nodeEnter.append('text')
.attr("dy", ".35em")
.attr("x", function(d) {
return d.children || d._children ? -13 : 13;
})
.attr("text-anchor", function(d) {
return d.children || d._children ? "end" : "start";
})
.text(function(d) { return d.data.name; });
// UPDATE
var nodeUpdate = nodeEnter.merge(node);
// Transition to the proper position for the node
nodeUpdate.transition()
.duration(duration)
.attr("transform", function(d) {
return "translate(" + d.y + "," + d.x + ")";
});
// Update the node attributes and style
nodeUpdate.select('circle.node')
.attr('r', 10)
.style("fill", function(d) {
return d._children ? "lightsteelblue" : "#fff";
})
.attr('cursor', 'pointer');
// Remove any exiting nodes
var nodeExit = node.exit().transition()
.duration(duration)
.attr("transform", function(d) {
return "translate(" + source.y + "," + source.x + ")";
})
.remove();
// On exit reduce the node circles size to 0
nodeExit.select('circle')
.attr('r', 1e-6);
// On exit reduce the opacity of text labels
nodeExit.select('text')
.style('fill-opacity', 1e-6);
// Update the links...
var link = svg.selectAll('path.link')
.data(links, function(d) { return d.id; });
// Enter any new links at the parent's previous position.
var linkEnter = link.enter().insert('path', "g")
.attr("class", "link")
.attr("id", function(d){
return ("link" + d.parent.id + "-" + d.id);
})
.attr('d', function(d){
var o = {x: source.x0, y: source.y0}
return diagonal(o, o)
});
// UPDATE
var linkUpdate = linkEnter.merge(link);
// Transition back to the parent element position
linkUpdate.transition()
.duration(duration)
.attr('d', function(d){ return diagonal(d, d.parent) });
// Remove any exiting links
var linkExit = link.exit().transition()
.duration(duration)
.attr('d', function(d) {
var o = {x: source.x, y: source.y}
return diagonal(o, o)
})
.remove();
// Stash the old positions for transition.
nodes.forEach(function(d) {
d.x0 = d.x;
d.y0 = d.y;
});
}
// Toggle children on click.
function mouseover(event, d) {
//reset all nodes color
d3.selectAll("circle").style("fill", "white");
d3.selectAll("path").style("stroke", "#c3c3c3");
while (d.parent) {
d3.selectAll("#node"+d.id).style("fill", "red")
if (d.parent != "null")
d3.selectAll("#link"+d.parent.id + "-" + d.id).style("stroke", "red")
d = d.parent;
}
}
// Creates a curved (diagonal) path from parent to the child nodes
function diagonal(s, d) {
path = `M ${s.y} ${s.x}
C ${(s.y + d.y) / 2} ${s.x},
${(s.y + d.y) / 2} ${d.x},
${d.y} ${d.x}`
return path
}
.node {
cursor: pointer;
}
.node circle {
fill: #fff;
stroke: steelblue;
stroke-width: 3px;
}
.node text {
font: 12px sans-serif;
}
.link {
fill: none;
stroke: #ccc;
stroke-width: 2px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.7.0/d3.min.js"></script>