How do I remove tinyMCE and then re-add it?

To cleanly remove an editor instance and avoid any errors use:

tinymce.EditorManager.execCommand('mceRemoveControl',true, editor_id);

To reinitialize the instance use:

tinymce.EditorManager.execCommand('mceAddControl',true, editor_id);

Be aware that when moving TinyMCE editors in the DOM you need to removeControl and addControl too, otherwise it results in JS errors.

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As of TinyMCE 4 the methods to remove and reinitialize an instance are now...

To cleanly remove an editor instance and avoid any errors use:

tinymce.EditorManager.execCommand('mceRemoveEditor',true, editor_id);

To reinitialize the instance use:

tinymce.EditorManager.execCommand('mceAddEditor',true, editor_id);

Late to the party but it might save someone the headache. Here's what worked for me on version 4.2.4 (2015-08-17):

tinymce.EditorManager.editors = []; 

Then I could re-init an editor on the same dynamically created div

tinymce.init({selector:"#text"});   

Edit : 2020-06-20

With version: 5.2.x, do

 tinymce.activeEditor.destroy();
 

or

 tinymce.remove('#myeditor');