Book Image

D3.js Quick Start Guide

By : Matthew Huntington
Book Image

D3.js Quick Start Guide

By: Matthew Huntington

Overview of this book

D3.js is a JavaScript library that allows you to create graphs and data visualizations in the browser with HTML, SVG, and CSS. This book will take you from the basics of D3.js, so that you can create your own interactive visualizations, to creating the most common graphs that you will encounter as a developer, scientist, statistician, or data scientist. The book begins with an overview of SVG, the basis for creating two-dimensional graphics in the browser. Once the reader has a firm understanding of SVG, we will tackle the basics of how to use D3.js to connect data to our SVG elements. We will start with a scatter plot that maps run data to circles on a graph, and expand our scatter plot to make it interactive. You will see how you can easily allow the users of your graph to create, edit, and delete run data by simply dragging and clicking the graph. Next, we will explore creating a bar graph, using external data from a mock API. After that, we will explore animations and motion with a bar graph, and use various physics-based forces to create a force-directed graph. Finally, we will look at how to use GeoJSON data to create a map.
Table of Contents (10 chapters)

Updating click points after a transform

Try zooming and panning and then clicking on the SVG to create a new run. You'll notice it's in the wrong place. That's because the SVG click handler has no idea that a zoom or pan has happened. Currently, if you click on the visual point, no matter how much you may have zoomed or panned, the click handler still converts it as if you had never zoomed or panned.

When we zoom, we need to save the transformation information to a variable so that we can use it later to figure out how to properly create circles and runs. Find the zoomCallback declaration and add var lastTransform = null right before it. Then add lastTransform = d3.event.transform; to the beginning of the function declaration. It should look as follows:

var lastTransform = null; //add this
var zoomCallback = function(){
lastTransform = d3.event.transform; //add...