We can do far more with D3 than just playing around with selections and changing the properties of the elements. We can change the properties of elements on the page.

With D3, we can change the contents of an element, add new elements, or remove elements we don't want.

Let's add a new column to the table from our preceding example:

const newCol = d3.selectAll('tr').append('td')

We selected all the table rows (which returned a new selection object) and then appended a new cell to each using the .append() selection. All D3 actions return the current selection, so we can chain actions or assign the new selection to a variable newCol  for later use.

We have an empty invisible column on our hands. Let's add some text to spruce things up:

newCol.text('a')

At least now that it's full of instances of a, we can say a column is present. However, that's kind of pointless, so let's follow the pattern set by other columns:

newCol.text((d, i) => ['Seven', 'u', 'j', 'm'][i])

The trick of dynamically defining the content via a function helps us pick the right string from a list of values depending on the column we're in, which we identify by the index i. Figured out the pattern, yet?

Similarly, we can remove elements using .remove(). For instance, to get rid of the last row in the table, you'd write something as follows:

d3.selectAll('tbody tr:last-child').remove()