Fix #519: Support in operator for useParams()

Author: kcirtaptrick

.changeset/nice-oranges-mate.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/router": patch
+---
+
+Support `in` operator for useParams()

src/utils.ts

@@ -158,6 +158,9 @@ export function createMemoObject<T extends Record<string | symbol, unknown>>(fn:
     },
     ownKeys() {
       return Reflect.ownKeys(fn());
+    },
+    has(_, property) {
+      return property in fn();
     }
   });
 }