D3 Visualization Basics — First Steps
In this small project, we will start with a simple div container with the class of “container”.
Right now this doesn’t do anything, so it’s not worth showing. But if D3 code is added to create a blue box, it might look a little more interesting. [Provided you find blue boxes interesting.]
Above is a simple example of a basic D3 procedure. It can helpful to think about this command as having two parts: getting a DOM [browser] element to manipulate and giving instructions for those manipulations. Here is what the code is doing:
- The select statement [
d3.selectAll()] code is finding every instance of the class of “container”. [There is only one element on the page.]
append()method adds another div as a child element inside of the container div.
attr()method gives the new div a class of “new-block”.
style()method gives the new div several style properties
text()method puts the text “Blue block” into the div
attr() methods can be a little confusing since they do similar things, but
attr() will place attributes in the HTML tag, while
style() writes in-line CSS for the element, which will override any CSS stylesheet you load in the header. These are just a few of the different methods you can use for a D3 DOM selection object, and you can find more in the D3 API reference.
Blue Block with Functions
Creating the blue block was a blast, but adding some functionality might make this a little more useful. Let’s make the block change color on a click and then remove it on a double click.
The first part of the script to create the blue block is the same, except I’ve doubled the code to have to blue blocks and I added new code that interacts with the blue block. The
on() method allows you to attach an event listener to elements rendered in the browser. These will wait until a certain event happens. In the example it executes a function to turn the box orange when the blue box is clicked. You can put many different instructions in here and aren’t limited to manipulating the element that is being clicked. Below is an illustration that I find useful for visualizing how event listeners are attached. I will devote another post to the details of D3 event listeners.
You might notice the
d3.select(this) in the code.
this in the code refers to the specific DOM element which was clicked or double clicked. If you click on the left block, only that block turns orange. You could change the code replace
'.block-new' and clicking one button will change both buttons to orange.
d3.select(this) code blocks in the event listener function makes it so they are only executed when the event happens. The block’s background color is changed to orange [#FF9821] when it’s clicked. The
remove() method deletes any DOM elements within the selection including the children elements. This comes in handy when you need to rebuild or update a data visualization.
Data! D3’s most powerful tool.