[wp-trac] [WordPress Trac] #31037: Uploading files through media modal causes error in < IE10

[WordPress Trac]

#31037: Uploading files through media modal causes error in < IE10
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 Reporter:  joehoyle      |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Media         |    Version:  4.1
 Severity:  normal        |   Keywords:
  Focuses:                |
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 Trying to upload a file in the Media Modal in IE9 and lower triggers a
 "File Download" popup because the "async-upload.php" endpoint now returns
 `Content-Type: application/json` since 4.1. IE9 and lower don't understand
 this content-type so trigger a file download dialogue.

 This was discussed at some length with the introduction of the new Media
 Modal here: https://core.trac.wordpress.org/ticket/22446#comment:20 long
 story short - returning `application/json` is not usually a problem as
 jQuery automatically handles it for older versions of IE, however this
 particular request is handled by Plupload which does not handle this edge
 case.

 Before https://core.trac.wordpress.org/changeset/30354 this endpoint
 returned `text/html` as it's Content Type; however now
 `wp_send_json_error` and associated functions are used which triggers a
 `Content-Type` header of `application/json`.

 I'm not sure what versions of IE is "officially" supported, but it would
 seem right now the upload file workflow feels broken in < IE10.

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Ticket URL: <https://core.trac.wordpress.org/ticket/31037>
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