Quick Fix for Wordpress Visual Editor blank / not working

gistfile1.php

if you open browser development tool's console and find some javascript errors like  "switchEditors is undefined" or "jquery is undefined", It appears that the new version of WordPress has some new performance optimisation features that concatenate all JavaScript resources into a single request.

Solution: put the following two lines of codes in wp-config.php:

define('CONCATENATE_SCRIPTS', false);
define('SCRIPT_DEBUG', true);