update the DOM manually as opposed through react rendering

react messes up the DOM sometimes because of, I assume, not
being aware of the changes to the real DOM by contenteditable.

src/editor/render.js

@@ -0,0 +1,52 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export function rerenderModel(editor, model) {
+    while (editor.firstChild) {
+        editor.removeChild(editor.firstChild);
+    }
+    for (const part of model.parts) {
+        editor.appendChild(part.toDOMNode());
+    }
+}
+
+export function renderModel(editor, model) {
+    // remove unwanted nodes, like <br>s
+    for (let i = 0; i < model.parts.length; ++i) {
+        const part = model.parts[i];
+        let node = editor.childNodes[i];
+        while (node && !part.canUpdateDOMNode(node)) {
+            editor.removeChild(node);
+            node = editor.childNodes[i];
+        }
+    }
+    for (let i = 0; i < model.parts.length; ++i) {
+        const part = model.parts[i];
+        const node = editor.childNodes[i];
+        if (node && part) {
+            part.updateDOMNode(node);
+        } else if (part) {
+            editor.appendChild(part.toDOMNode());
+        } else if (node) {
+            editor.removeChild(node);
+        }
+    }
+    let surplusElementCount = Math.max(0, editor.childNodes.length - model.parts.length);
+    while (surplusElementCount) {
+        editor.removeChild(editor.lastChild);
+        --surplusElementCount;
+    }
+}