D3.js

Introduction

D3.js is a javascript library developed by Mike Bostock (which was very proficient, giving a lot of examples). It basically uses an HTML <div> to create a SVG and use javascript to draw and update the svg components. You dynamically create those elements within a pre-defined canvas and those elements can be customized via CSS.

I used it for a graph network of kanji bubbles sylhare/kanji:

kanji-graph.png

When I was saying that author Mike Bostock was very proficient, you can check all of his examples on:

With each new version of D3.js the syntax can change a bit (even though the overall logic stays similar). It can be quite confusing looking at some example, not knowing how to “translate” it from one version to another. Here I use ** D3.js v4**, it provided a good amount of examples and was not the oldest.

Check D3 in Depth to learn it.

Basic structure

The whole process is called a simulation, for the node graph:

  • you give the data (nodes, links between those nodes)
  • you set the layout of those elements (css, svg, other attributes …)
  • you set some constraints (force, gravity, …)
  • you may add some other logic or added components to it

And then you run the simulation which will make the system move.

Examples

For these examples I’ve got inspired by all those talented people on the internet that provided cool examples. If you have one other site to check that was no mentioned before, I’d recommend Yan Holtz which provides amazing and simple examples at d3-graph-gallery.com

With data

You create a svg within the div of id “d3example” with defined height and width

var svg = d3.select("#d3example")
    .append("svg")
    .attr("width", width)
    .attr("height", height);

Then you can load the nodes from the your example data (a json). You put all the elements in the svg group “g” and select all nodes from that data.

var exampleData = [{ "name": "A" }, { "name": "B" }, { "name": "C" }, { "name": "D" }];
var node = svg.append("g")
    .selectAll("nodes")
    .data(exampleData)
    .enter();

You append a svg circle object to each of the node, and specify some svg attributes We put the coordinates to some random numbers inside our canvas:

var circles = node.append("circle")
      .attr("cx", () => {return Math.random() * width})
      .attr("cy", () => {return Math.random() * height})
      .attr("r", 40)
      .style("fill", rgb(239, 192, 80))

If you want to look at how the HTML is constructed, click on Details to expand the html. Basically like: div > svg > g > circle

<div id="d3example"> 
    <svg width="450" height="450">
        <circle cx="225" cy="225" r="40" style="fill: rgb(239, 192, 80)"></circle>
        <circle cx="..." cy="..." r="40" style="fill: rgb(239, 192, 80)"></circle>
    </svg>
</div>

Miscellaneous

Some other things you may want to know using d3.js

Transition

You can transition to ease the update using the d3.transition() method:

var t = d3.transition().duration(750);

Then you can use this transition on the nodes to make their attributes transitioned from their current state to their desired state.

// the node will shrink (transition) to a radius of 1e-6 then disappear
node_up.exit()
    .transition(t)
    .attr("r", 1e-6)
    .remove();

Interval

When you want to update your canvas at a set interval. You may use another d3 method called d3.interval() which works as a timeout:

d3.interval(() => restart(randomizeData()), 2000);

Here it will restart with random data the simulation every 2000 seconds

Colors

You can use d3 automatic colors for your nodes using d3-scale-chromatic, it provides a lot of flexibility.

const d3Color = d3.scaleOrdinal(d3.schemeCategory20);
d3Color(Math.random())

It uses scaleOrdinal that creates a color scale using a color scheme (that I’m just using randomly for demo).

Other examples

You can check some other examples here: