ACF Uncaught TypeError: Cannot read property ‘id’ of undefined

Recently I was working on a site using Advanced Custom Fields (ACF) but the field input boxes had stopped working.

In the browser console, I saw the error

ACF Uncaught TypeError: Cannot read property ‘id’ of undefined

Advanced Custom Fields and Select2

Advanced Custom Fields uses the Select2 library (version 4), however another plugin was loading Select2 (version 3). WordPress loaded the first one registered which happened to be version 3, which caused the problem.

This ACF support thread about Uncaught TypeError: Cannot read property 'id' of undefined, was helpful in diagnosing this issue.

Solution

Deactivating the plugin loading Select2 version 3 is a short-term solution. Then hopefully, you can then update the offending plugin to a newer version that uses Select2 version 4 or find another plugin.

Sal Ferrarello (@salcode)

Sal is a PHP developer with a focus on the WordPress platform. He is a conference speaker with a background including Piano Player, Radio DJ, Magician/Juggler, Beach Photographer, and High School Math Teacher. Sal can be found professionally at WebDevStudios, where he works as a senior backend engineer.