Fix view source and devtools showing hljs warnings (#7759)

src/utils/JSON.ts

@@ -0,0 +1,32 @@
+/*
+Copyright 2022 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.
+*/
+
+type StringifyReplacer = (this: any, key: string, value: any) => any;
+
+// From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value#circular_references
+// Injects `<$ cycle-trimmed $>` wherever it cuts a cyclical object relationship
+export const getCircularReplacer = (): StringifyReplacer => {
+    const seen = new WeakSet();
+    return (key: string, value: any): any => {
+        if (typeof value === "object" && value !== null) {
+            if (seen.has(value)) {
+                return "<$ cycle-trimmed $>";
+            }
+            seen.add(value);
+        }
+        return value;
+    };
+};