Replace react-router-scroll-4 with inlined implementation (#36253)

app/javascript/mastodon/containers/scroll_container/state_storage.ts

@@ -0,0 +1,46 @@
+import type { LocationBase, ScrollPosition } from 'scroll-behavior';
+
+const STATE_KEY_PREFIX = '@@scroll|';
+
+interface LocationBaseWithKey extends LocationBase {
+  key?: string;
+}
+
+/**
+ * This module is part of our port of https://github.com/ytase/react-router-scroll/
+ * and handles storing scroll positions in SessionStorage.
+ * Stored positions (`[x, y]`) are keyed by the location key and an optional
+ * `scrollKey` that's used for to track separately scrollable elements other
+ * than the document body.
+ */
+
+export class SessionStorage {
+  read(
+    location: LocationBaseWithKey,
+    key: string | null,
+  ): ScrollPosition | null {
+    const stateKey = this.getStateKey(location, key);
+
+    try {
+      const value = sessionStorage.getItem(stateKey);
+      return value ? (JSON.parse(value) as ScrollPosition) : null;
+    } catch {
+      return null;
+    }
+  }
+
+  save(location: LocationBaseWithKey, key: string | null, value: unknown) {
+    const stateKey = this.getStateKey(location, key);
+    const storedValue = JSON.stringify(value);
+
+    try {
+      sessionStorage.setItem(stateKey, storedValue);
+    } catch {}
+  }
+
+  getStateKey(location: LocationBaseWithKey, key: string | null) {
+    const locationKey = location.key;
+    const stateKeyBase = `${STATE_KEY_PREFIX}${locationKey}`;
+    return key == null ? stateKeyBase : `${stateKeyBase}|${key}`;
+  }
+}