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Event Question Editor API


Triggered when current state of Undo/Redo changes. State changes are triggered by the following actions:

  • Clicking the Undo or Redo buttons.
  • Calling undo() or redo() public methods.
  • Changing any UI field (on blur).
Use this event to manage custom button states (i.e. if not using default undo/redo buttons).

This event gets fired twice per state change:

  • The first event fires with both booleans set to false, to indicate both buttons should be disabled (see right).
  • The second event fires with updated states once the first has completed. E.g. after changing a field, canUndo will be true and canRedo will be false (see right).

New snapshots are typically very fast so both events will trigger rapidly, but undo/redo operations can take some time. It is important to listen to these events and prevent or ignore further undo/redo commands until the current operation completes.

Note if you call the public method off() with the argument revisionHistoryState:change, it will disable the default undo and redo buttons.

Callback arguments

  • undo_state object
    An object that contains:
    • canUndo: boolean, indicates whether there is a previous state that QE can be reverted to via the undo() public method.
    • canRedo: boolean, indicates whether there is a newer state that QE can be restored to via redo() public method.
    Sample data:
    (first event): {canUndo: false, canRedo: false}
    Sample data (second event): {canUndo: true, canRedo: false}
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