Changes

frontend/src/lib/collections.ts

@@ -0,0 +1,15 @@
+export function appendUnique<T>(
+	current: T[],
+	incoming: T[],
+	keyOf: (item: T) => string | number
+): T[] {
+	const seen = new Set(current.map(keyOf));
+	const added: T[] = [];
+	for (const item of incoming) {
+		const key = keyOf(item);
+		if (seen.has(key)) continue;
+		seen.add(key);
+		added.push(item);
+	}
+	return added.length > 0 ? [...current, ...added] : current;
+}