From 3ad5c9f9c1b6b0af584cc7ba6841f97f0011debf Mon Sep 17 00:00:00 2001
From: jos <wjosdejong@gmail.com>
Date: Mon, 17 Feb 2020 20:08:16 +0100
Subject: [PATCH] Fix #908: editor throwing an exception when switching from
 `'preview'` to `'code'` mode

---
 HISTORY.md            | 6 ++++++
 docs/api.md           | 2 +-
 src/js/previewmode.js | 6 ++++--
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/HISTORY.md b/HISTORY.md
index 87a8e63..6e4560e 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -3,6 +3,12 @@
 https://github.com/josdejong/jsoneditor
 
 
+## not yet published, version 8.6.1
+
+- Fix #908: editor throwing an exception when switching from `'preview'`
+  to `'code'` mode.
+
+
 ## 2020-02-16, version 8.6.0
 
 - Fixed #906: Implemented turning Python objects containing `True`, `False` 
diff --git a/docs/api.md b/docs/api.md
index 6310649..ef47c3c 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -230,7 +230,7 @@ Constructs a new JSONEditor.
 
 - `{boolean} history`
 
-  Enables history, adds a button Undo and Redo to the menu of the JSONEditor. `true` by default. Only applicable when `mode` is 'tree' or 'form'.
+  Enables history, adds a button Undo and Redo to the menu of the JSONEditor. `true` by default. Only applicable when `mode` is `'tree'`, `'form'`, or `'preview'`.
 
 - `{String} mode`
 
diff --git a/src/js/previewmode.js b/src/js/previewmode.js
index 7b3c6be..c5dc994 100644
--- a/src/js/previewmode.js
+++ b/src/js/previewmode.js
@@ -424,8 +424,10 @@ previewmode.destroy = function () {
 
   this._debouncedValidate = null
 
-  this.history.clear()
-  this.history = null
+  if (this.history) {
+    this.history.clear()
+    this.history = null
+  }
 
   // Removing the FocusTracker set to track the editor's focus event
   this.frameFocusTracker.destroy()