[wp-trac] [WordPress Trac] #31901: JS error while post editing

[WordPress Trac]

#31901: JS error while post editing
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 Reporter:  m_i_n                           |      Owner:
     Type:  defect (bug)                    |     Status:  new
 Priority:  normal                          |  Milestone:  Awaiting Review
Component:  General                         |    Version:  trunk
 Severity:  normal                          |   Keywords:
  Focuses:  ui, javascript, administration  |
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 Hi,
 since version WP 4.2 beta 2 (probably), there is an error in JS console
 while editing post: http://i.imgur.com/IE96L5K.png (TypeError: c is
 undefined).
 It makes editing post/page basically impossible.
 It doesn't occur always, though. Mostly after full page refresh (ctrl+f5),
 but not always. Often enough to make it impossible to work on posts.
 My test environment is:
 - WP 4.2-beta4-32021
 - standard theme (doesn't matter which one)
 - dummy content imported
 - all plugins off

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Ticket URL: <https://core.trac.wordpress.org/ticket/31901>
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