Text Selection Particle Effects

This was originally posted on my blog.

After reading Playing With Particles Using the Web Animations API I wondered if it would be possible to create particle effects based on the user selecting text.

You could whip up something quick by listening for a mousedown event and adding the particles based on the mouse position. It looks cool, but I wasn't too happy because it doesn't look as neat, and it doesn't work if you're doing selection with the keyboard.

There are two events we need to make this work:

• selectstart
• selectionchange

selectstart is needed to reset our initial top position. We use this to check if we're moving up or down in our selection. Once a selection is finished, and we start again, and the value can be reset.

selectionchange is fired any time our selection changes, and we'll use this to generate our coordinates for our particles. This is where most of the work is done.

Here's how it goes:

1. We start selecting some text, and selectstart is fired, where we reset our initial top value to null
2. selectionchange is then fired where get the current selection using window.getSelection()
3. With this, we get the range of text using selection.getRangeAt(0), followed by the bounds using range.getClientRects()
4. The bounds now contain a DOMRectList with our selections, and we're only interested in the first and last item in this list
5. If our initial top value isn't set (as it's been reset by selectstart) then we assign it to the top value of the first DOMRect item in the list
6. We check if the left value has changed in the most recent DOMRect item in the list
7. We check if we're moving up or down the page with our selection
8. If we're moving down, we use the most recent DOMRect in the list, otherwise, we use the first
9. If we're moving left, our x position will be the left value, otherwise, we'll use right
10. Our y value will be the y value of our chosen bounds, plus the height of the selection so the particles appear below the text

Thanks to Louis Hoebregts for a great article. I had a bunch of fun and confusion getting this to work, but it was a welcome distraction.