Create DOM Elements with D3 v4

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Published 7 years ago
Updated 5 years ago

Change is good, but creating from scratch is even better. This lesson shows you how to create DOM elements from D3 and insert them into your document as needed. You’ll officially be on your way to creating data visualizations!

[00:00] We've now seen how to modify an existing document, but let's look at how we can actually create new elements from our D3 code as well. We've got our div here with a class of title. I'm going to change this first line here to, and then we can get rid of this. We're not worried about that anymore, and we can get rid of this.

[00:22] What I'm actually going to do here is, I'm going to append a new button. I'm saying select the div, append a new button. Now this HTML method call is going to be affecting this button that we create.

[00:39] If we save this, we can see that our products link goes back to normal. We now have a button whose inner HTML is inventory, and then a bold sale. This is pretty simple. One thing to note here is that this method of append and the other methods we're going to look at here, are actually changing the selection.

[01:02] here is going to return a selection that is this whole div that's inside of our border. Once we say .append, that's going to return a new selection. Any statements that come after this line are going to affect that new selection.

[01:24] There's actually a convention in the D3 world where anything that creates a new selection is generally indented two spaces, and anything that operates on an existing selection is indented four spaces. If we're going to follow that, we would indent this.

[01:44] In this case, it's not going to provide a whole lot of benefit. If we were creating multiple items in the same statement, then it becomes useful in seeing where you're changing the objects that are actually being operated on.

[01:59] In addition to appending, you can actually insert elements. If we change this to insert, it's not going to look any different. By default, it's going to put it at the end. There's a second argument to insert, which is a before selector.

[02:14] If we were to say A:first-child here, we're telling it we want you to insert this button before the first child. We can see here that it does, in fact, get added to the beginning. We could change this to an nth child thing, where we say nth child two, and we put in the second position there, or we put it before the second child.

[02:35] That's how insert works. It allows you to specify where you want something created. The other thing to note is just that this first argument to insert, or the argument to append, can be any element name. It's essentially like you're calling document.createElement, and passing in that type.

[02:54] We could say div, and it's just going to create another div here. You get the idea. You can also remove elements from the DOM with D3. We could say, and remember this last link that we have here outside of our div has a class of action.

[03:10] We could say, and it will actually remove that link from the page. Whatever selection you have created here, if you then call remove, it's actually going to remove that from the document.

[03:27] To show an example of this convention here that we talked about, let's do this. We'll change this back to append, so that we've only got one argument here to worry about. We're saying select that title div, append a new div, set its HTML to inventory sale.

[03:45] We can also set a style on it. We'll just say style color, red. There, it's moved down to the end, since we changed it back to append. We're setting the style, setting the HTML, and now we're going to unindent one level because we're going to create another item here.

[04:02] This time, we'll go back to creating a button. Maybe let's just say the text is submit. There, we get a button added. It's on the same line there, since it's an in-line object. We can actually say .style, display, block.

[04:20] Now we've got that on its own line there. You can see here, when you have multiple things being created in a single statement, it becomes useful to be able to easily tell, "OK, we're creating a new selection here because it's only indented two." Then these lines are affecting that selection.

[04:38] Here, we're back to a two-space indent. That means we're creating a new selection by appending this button. Then these two lines are going to affect that selection. It just makes the code a little bit easier to understand. It's good to know, because you'll see a lot of examples that use this convention.

~ 6 years ago

The other commenters might have been saying the same thing, but I'm trying to understand whether the second .append is applying to the 'title' or to the 'div'?

In other words, how is the second append different to the .html just above it? It is applying to the same thing (the div), in which case (as other said) it should be intented the same?

Since you make such a point of this, I think that if you have it wrong in the video, you should fix it.