Capturing the expand and collapse event on a jQuery Mobile collapsible set

This morning over at I needed to capture the expanding/collapsing of a jQuery Mobile collapsible set. I wanted to add a class to an element, but only when a a specific set was opened. I Googled for a few minutes before finding a post over on the jQuery Mobile forums. Turns out it's pretty simple. Here's what I did.

In our case we're using form tags as the container, so that's what I bound my event to. I only cared about the expand event since I wanted to target the opening of a specific container, namely the Phone section. Next I used simple JavaScript property access ( to check the id if the current target. Finally I added and removed a class as needed.

Pro-tip: Rather than applying a large number of attributes to an element with jQuery's css() method, consider creating a class for those styles. Then using the addClass()/removeClass() partner methods to add and remove the styling. Much simpler and it keeps your CSS out of your JavaScript code.