add function

src/lib/utils/functions.ts

@@ -77,6 +77,10 @@ export function randomString() {
     return Math.random().toString(36).substring(2, 9);
 }
 
+export function isJustOne<T>(list: T[]): list is [T] {
+    return list.length === 1;
+}
+
 export function trackByFactory<T extends ITrackable<PrimaryKey>, PrimaryKey extends Id = T['id']>() {
     return (_index: number, item: T): Id => item.id;
 }