Quickie: Fading in a newly created element using CSS

Update: I got an email from James at VIDesignz who found another solution to this problem using the :empty selector. I added it at the end of the article.

As part of our JSFoo workshop today I was asked to look into an issue a team had that you can not apply a CSS transition to a newly created element when you change the CSS settings in JavaScript. As I was dealing with professionals, they created a simple JSFiddle to show the problem:

As you see just changing the property (in this case the opacity) is not enough to have a transition. There are a few solutions to this shown in the Fiddle, too, like forcing a reflow, which of course could be a terrible idea.

I played with this and found the solution to be to not change the properties in JavaScript (which is kind of dirty anyways) but leave it all to CSS instead. The biggest part of the solution is not to use a transition but an animation instead and trigger it by applying a class to the newly created element right after adding it to the DOM:

Update: As mentioned by Kyle Simpson on Twitter, there is a way to do the same with a transition, but you need to wrap the creation and applying the class into requestAnimationFrame calls which in turn means some polyfilling:

Update2 You can also use the :empty selector in CSS to achieve the same when you add the new element as a child: