add mountView utility to handle error handling on mount

and use it where errorToDOM is used currently for catching mount errors

src/platform/web/ui/general/ListView.js

@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {el} from "./html.js";
-import {errorToDOM} from "./error.js";
+import {mountView} from "./utils.js";
 
 function insertAt(parentNode, idx, childNode) {
     const isLast = idx === parentNode.childElementCount;
@@ -108,12 +108,7 @@ export class ListView {
         for (let item of this._list) {
             const child = this._childCreator(item);
             this._childInstances.push(child);
-            try {
+            fragment.appendChild(mountView(child, this._mountArgs));
-                const childDomNode = child.mount(this._mountArgs);
-                fragment.appendChild(childDomNode);
-            } catch (err) {
-                fragment.appendChild(errorToDOM(err));
-            }
         }
         this._root.appendChild(fragment);
     }
@@ -122,13 +117,7 @@ export class ListView {
         this.onBeforeListChanged();
         const child = this._childCreator(value);
         this._childInstances.splice(idx, 0, child);
-        let node;
+        insertAt(this._root, idx, mountView(child, this._mountArgs));
-        try {
-            node = child.mount(this._mountArgs);
-        } catch (err) {
-            node = errorToDOM(err);
-        }
-        insertAt(this._root, idx, node);
         this.onListChanged();
     }
 

src/platform/web/ui/general/TemplateView.js

@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import { setAttribute, text, isChildren, classNames, TAG_NAMES, HTML_NS } from "./html.js";
-import {errorToDOM} from "./error.js";
+import {mountView} from "./utils.js";
 import {BaseUpdateView} from "./BaseUpdateView.js";
 
 function objHasFns(obj) {
@@ -282,17 +282,11 @@ class TemplateBuilder {
         return node;
     }
 
-    // this insert a view, and is not a view factory for `if`, so returns the root element to insert in the template
+    // this inserts a view, and is not a view factory for `if`, so returns the root element to insert in the template
     // you should not call t.view() and not use the result (e.g. attach the result to the template DOM tree).
     view(view, mountOptions = undefined) {
-        let root;
-        try {
-            root = view.mount(mountOptions);
-        } catch (err) {
-            return errorToDOM(err);
-        }
         this._templateView.addSubView(view);
-        return root;
+        return mountView(view, mountOptions);
     }
 
     // map a value to a view, every time the value changes

src/platform/web/ui/general/utils.js

@@ -0,0 +1,27 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+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.
+*/
+
+import {errorToDOM} from "./error.js";
+
+export function mountView(view, mountArgs = undefined) {
+    let node;
+    try {
+        node = view.mount(mountArgs);
+    } catch (err) {
+        node = errorToDOM(err);
+    }
+    return node;
+}