Changed 76 to a P/S

Author: mattpocock

src/09-external-libraries/76-react-query.explainer.ts renamed to src/09-external-libraries/76-react-query.problem.ts

@@ -0,0 +1,53 @@
+import { useQuery } from "@tanstack/react-query";
+import { Equal, Expect } from "../helpers/type-utils";
+
+interface User {
+  fullName: string;
+  job: string;
+}
+
+const getUser = async (): Promise<User> => {
+  return Promise.resolve({
+    fullName: "Matt Pocock",
+    job: "Developer",
+  });
+};
+
+/**
+ * A bit of a hint to start with. useQuery has a LOT of overloads - but a lot
+ * of them are disappearing in the next major version. The ones that'll be
+ * sticking around are the first three.
+ *
+ * 1. How are the first three overloads different to the others? Put differently,
+ * what's the thing that's similar about the first three that's different to
+ * the other six?
+ */
+
+useQuery;
+// ^ CMD+click on this to see the overloads
+
+/**
+ * 2. When you provide queryFn to useQuery, the type of query.data is inferred
+ * as the return type of queryFn. Why is that?
+ */
+const query1 = useQuery({
+  queryFn: getUser,
+});
+
+// Without initialData, the type of query1.data is User | undefined
+type test1 = Expect<Equal<typeof query1.data, User | undefined>>;
+
+/**
+ * 3. When you provide initialData to useQuery, the type of query.data no longer
+ * has undefined in it. Why is that?
+ */
+const query2 = useQuery({
+  queryFn: getUser,
+  initialData: {
+    fullName: "",
+    job: "",
+  },
+});
+
+// WITH initialData, the type of query.data is just User
+type test2 = Expect<Equal<typeof query2.data, User>>;