Destroy preview list's previous operations when populating new ones

spec/extensions/command-panel-spec.coffee

@@ -241,6 +241,10 @@ describe "CommandPanel", ->
         rootView.trigger 'command-panel:toggle-preview' # ensure we can close panel without problems
         expect(commandPanel).toBeHidden()
 
+      it "destroys previously previewed operations if there are any", ->
+        waitsForPromise -> commandPanel.execute('X x/b+/')
+        # there shouldn't be any dangling operations after this
+
     describe "if the command is malformed", ->
       it "adds and removes an error class to the command panel and does not close it", ->
         rootView.trigger 'command-panel:toggle'

src/extensions/command-panel/preview-list.coffee

@@ -15,7 +15,9 @@ class PreviewList extends View
 
   hasOperations: -> @operations?
 
-  populate: (@operations) ->
+  populate: (operations) ->
+    @destroyOperations() if @operations
+    @operations = operations
     @empty()
     @html $$$ ->
       for operation in operations
@@ -28,7 +30,6 @@ class PreviewList extends View
             @span suffix
 
     @setSelectedOperationIndex(0)
-
     @show()
 
   selectNextOperation: ->
@@ -55,6 +56,10 @@ class PreviewList extends View
   getOperations: ->
     new Array(@operations...)
 
+  destroyOperations: ->
+    operation.destroy() for operation in @getOperations()
+    @operations = null
+
   getSelectedOperation: ->
     @operations[@selectedOperationIndex]