Solving Undefined Property Error with wp.data.select('meta') in WordPress Gutenberg

Learn how to handle undefined properties in your WordPress Gutenberg meta-boxes and ensure post validation before publication.
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This video is based on the question https://stackoverflow.com/q/67808739/ asked by the user 'Jandon' ( https://stackoverflow.com/u/6696150/ ) and on the answer https://stackoverflow.com/a/67814025/ provided by the user 'Sally CJ' ( https://stackoverflow.com/u/9217760/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving Undefined Property Error with wp.data.select('meta') in WordPress Gutenberg

If you’re using the Gutenberg editor in WordPress, you might have encountered some challenges while checking whether specific fields—such as the featured image, title, and a custom text field—are filled out before a user can publish their post. Specifically, you may have run into an error such as Uncaught TypeError: Cannot read property '_myprefix_text_metafield' of undefined. In this guide, we’ll explore the cause of this error and how to resolve it effectively.

The Problem Explained

When you attempt to verify that your required fields are not empty, you may face issues if the metadata is not yet accessible. One common scenario is when the asynchronous XHR/AJAX request fetching post data from the REST API hasn't fully resolved, which means that the getEditedPostAttribute('meta') call may return undefined, leading to the error you’re experiencing.

Context of the Issue

In your current setup, you're checking the fields as follows:

[[See Video to Reveal this Text or Code Snippet]]

This works fine for checking existing values, but can lead to errors if the metadata has not loaded completely. Thus, trying to access _myprefix_text_metafield when getEditedPostAttribute('meta') returns undefined triggers a type error.

The Solution: Improved Code Implementation

To resolve this issue, you need to ensure that your call to access metadata checks whether the metadata itself is defined before trying to access any property. This can be done through optional chaining or condition checks.

Updated Code Snippet

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of Changes Made

Optional Chaining: By adding the ? after getEditedPostAttribute('meta'), we are implicitly checking if meta is defined before trying to access _myprefix_text_metafield. This prevents the TypeError when meta is indeed undefined.

Condition Checks: To confirm if the field is empty, the condition undefined !== textPresentation && !textPresentation is checking if textPresentation has a value that is not undefined as well as not being empty. If either condition fails, the lock on the post will be triggered.

Conclusion

By implementing the improvement above, you should be able to validate and enforce rules on your post creation workflow without encountering the undefined property errors. This enhancement not only secures the ‘Publish’ button functionality but also improves the user experience by ensuring all necessary information is provided before a post goes live.

Make sure to always handle asynchronous operations carefully to avoid encountering undefined results in your JavaScript code. Happy coding with Gutenberg!