Upgrade to 4.2.1 and now can't switch between text and visual editor

Have you tried:

• flushing any caching plugins you might be running, as well as server and/or browser caches.
• deactivating all plugins (yes, all) to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s). If you can’t get into your admin dashboard, try resetting the plugins folder by FTP or PhpMyAdmin (read “How to deactivate all plugins when you can’t log in to wp-admin” if you need help). Sometimes, an apparently inactive plugin can still cause problems. Also remember to deactivate any plugins in the mu-plugins folder. The easiest way is to rename that folder to mu-plugins-old
• switching to the Twenty Fifteen theme to rule out any theme-specific problems. If you can’t log in to change themes, you can remove the theme folders via FTP so the only one is twentyfifteen. That will force your site to use it.
• manually upgrading. When all else fails, download a fresh copy of the latest.zip file (top right on this page) to your computer, and use that to copy up. You may need to delete the wp-admin and wp-includes folders on your server. Read the Manual Update directions first.

I’ll try the manual update now and get back to you.

Uncaught ReferenceError: switchEditors is not defined is most often caused by a plugin.

You can also go to the area that is the problem. In Chrome upper right corner go to more tools and then javascript console. Try to switch editors and see if anything shows up.

You can also change this line in the wp-config.php file from define('WP_DEBUG', false); to define('WP_DEBUG', true);

Ok, so no luck so far. Here is what I have done.

Deactivated all plugins: Problem persisted
Manually updated wordpress to 4.2.1: Problem persisted

Debug log doesn’t give me any helpful information. Please help.

I’ve also noticed that several of the buttons on the edit page don’t seem to be responding or throwing any errors

>Add Media
>screen option
>help
>any of the expand/compress arrows

Please help!

[ No bumping please. ]

Any errors on the edit page are usually javascript conflicts. Go to the editor, open (in Chrome, more tools>>JavaScript console and see if that finds anything.

Also please post a URL in this format. sitename the word dot and com.

Update time: Ok. So I’ve solved one problem, but created another one

WARNING: This solution created other problems, but I think this will help to figure out where the problem was at

It appears that the issue was a database corruption that occurred when I did the update. The update was causing a significant lag when I tried to go to an edit screen in the admin menu. The lag, I believe, was causing the javascript to incorrectly load and or timeout. I backed up my database in cpanel and then using pypAdmin, I optimized only the tables that showed overhead issues. This caused all of my featured image thumbnails to delink (more on this later). I then went to revert back to the pre-optimized database. The delinked featured images is still a problem but my admin page lag and visual editor/text editor issue is now solved. I’m going to close this issue and open a new one for the feature thumbnail issue now.