Console js error while loading Customizer(Uncaught TypeError: Cannot read property 'action' of null)

[coderarjun]

This form is for reporting bugs in WordPress 4.9.1

• When loading customizer, there is found console js error in WordPress 4.9.1, screenshot at ​http://prntscr.com/hjsq3i

Note:

• This error is found in WordPress Customizer Version 4.9.1, it's an error due to WP 4.9.1, not on themes.

Thank You

[adamsilverstein]

Hello @coderarjun - thanks for your bug report and welcome to WordPress trac!

I tried to reproduce this locally and do not see the errors you mentioned. Do you get the errors right away on load?

Can you please try accessing the customizer again with all plugins disabled and a default theme active? Also, please do a 'hard refresh' (shift + reload) to ensure you get fresh JavaScript -sometimes these files can get cached by your browser and do odd things.

Thanks.

[garrett-eclipse]

I noticed this throughout my wp-admin as well. After troubleshooting I determined it was caused by the Grammarly Chrome extension and would assume you're experiencing something similar. This is a new issue with 4.9. Let me know if this should be opened with Grammarly instead.
Thanks

[dingo_bastard]

I can confirm as well that this is the Grammarly issue. If you expand the error in the console, you'll see that Grammarly is causing this.

I'll report this to Grammarly.

[garrett-eclipse]

Thanks @dingo_bastard that reminds me I opened with Grammarly previously as well and they're aware of the issue, comment from their support;

Please rest assured that the technical team is aware of the problem and they are currently working on it.

Unfortunately, this will not be a quick fix and I cannot provide you with an estimated timeframe, as the developers will need some time to analyze the cause of this issue.

I’m going to close this case, but if you have further information regarding this issue, please reply to this email and the case will be re-opened for further investigation. We apologize for any inconvenience caused.

[dingo_bastard]

Haha I've just gotten the same mail... Seems like a template answer sadly. We'll see if they publish a fix for the extension.

[afercia]

See follow up in #43005. Seems this is not specifically related to Grammarly but can happen with any plugin passing an empty message to postMessage() which then gets parsed with $.parseJSON().

You can reproduces this at any time just pasting this in your console (use your site url):
postMessage( '', 'http://src.wordpress-develop.test/' )