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CSS

Posted by Alfons Pineda
Alfons Pineda
Courses Plus Student 1,287 Points

What's the difference between these selectors?

:nth-child :first-of-type :only-of-type

I watched the video explaining these, but I don't get the difference very much. Could someone explain?

2 Answers

Nick Pettit
STAFF
Nick Pettit
Treehouse Teacher
Nick Pettit
Nick Pettit
Treehouse Teacher

Hi Alfons,

  • :nth-child takes an integer value that allows you to select a child element. For example, if you have a <ul> with list items and you want to only select the 3rd item, you can do it with :nth-child instead of applying a class or ID to the 3rd item. Here's an example on CodePen that shows this in action: http://codepen.io/nickpettit/pen/FnejA
  • :first-of-type is a little tricky to explain in words, but it matches the first element that is of the type described in the selector. For example, if there were several nested <section> elements that also had siblings of other types, and you just wanted to select the first <section> (and not the first element) then you want :first-of-type. Here's an example on CodePen: http://codepen.io/nickpettit/pen/wiGrq
  • :only-of-type is similar to the previous example, except it will select elements only if they have no other similar siblings. Here's the same example in CodePen: http://codepen.io/nickpettit/pen/xKHdf - In this example, try changing header to section, and you'll see that it doesn't select the section elements. That's because there are multiples. However, there's only one header.

I hope that helps!

Alfons Pineda
Alfons Pineda
Courses Plus Student 1,287 Points

Amazing, thanks Nick! I now understand these concepts.

I am impressed that the staff and mods of Treehouse will actually answer and participate on the forums. This is truly a great site.

Nick Pettit
Nick Pettit
Treehouse Teacher
Nick Pettit
Nick Pettit
Treehouse Teacher

No problem, happy to help! :)

Nick Pettit
Nick Pettit
Treehouse Teacher
Nick Pettit
Nick Pettit
Treehouse Teacher

Weird, thanks James! Fixed it.

James Barnett
James Barnett
39,199 Points
James Barnett
James Barnett
39,199 Points

TL;DR - Any time you are confused on what a CSS selector does you can always use the SelectORacle, which is where I got the wording for the explanations here.

First some background ...

Parent & children in CSS:

Siblings in CSS:

Descendants in CSS:

Now that the background is covered here are some examples:

div:nth-child(2) p

Selects any p element that is a descendant of a div element that is a second child.

div p:first-of-type

Selects any p element that is a first child of its type that is a descendant of a div element.

span:only-of-type

Selects any span element that has no siblings of its type.

Here's a quick demo to see how this would work.

Images shamelessly lifted from the most excellent Selectutorial

Alfons Pineda
Alfons Pineda
Courses Plus Student 1,287 Points

That was an excellent explanation as well. Thanks!