Changed 74 solution

Author: mattpocock

src/09-external-libraries/74-react-hook-form-wrapper.solution.tsx renamed to src/09-external-libraries/74-react-hook-form-wrapper.solution.1.tsx

@@ -1,17 +1,8 @@
 import { DefaultValues, FieldValues, useForm } from "react-hook-form";
 import { Equal, Expect, Extends } from "../helpers/type-utils";
 
-/**
- * We add TValues as a generic to our hook, and use it to type the defaultValues.
- *
- * We constrain it to FieldValues so that it's assignable to useForm's defaultValues.
- */
 const useCustomForm = <TValues extends FieldValues>(defaultValues: TValues) => {
   const form = useForm({
-    /**
-     * There's a strange papercut here where we have to cast defaultValues as
-     * DefaultValues<TValues> to get it to work.
-     */
     defaultValues: defaultValues as DefaultValues<TValues>,
   });
 

src/09-external-libraries/74-react-hook-form-wrapper.solution.2.tsx

@@ -0,0 +1,61 @@
+import {
+  DefaultValues,
+  FieldValues,
+  UseFormGetValues,
+  UseFormHandleSubmit,
+  UseFormRegister,
+  useForm,
+} from "react-hook-form";
+import { Equal, Expect, Extends } from "../helpers/type-utils";
+
+const useCustomForm = <TValues extends FieldValues>(
+  defaultValues: TValues,
+): {
+  register: UseFormRegister<TValues>;
+  handleSubmit: UseFormHandleSubmit<TValues>;
+  getValues: UseFormGetValues<TValues>;
+} => {
+  const form = useForm({
+    defaultValues: defaultValues as DefaultValues<TValues>,
+  });
+
+  return {
+    register: form.register,
+    handleSubmit: form.handleSubmit,
+    getValues: form.getValues,
+  };
+};
+
+// ---- TESTS ----
+
+// @ts-expect-error defaultValues is required
+useCustomForm();
+
+useCustomForm(
+  // @ts-expect-error defaultValues must be an object
+  2,
+);
+
+const customForm = useCustomForm({
+  firstName: "",
+  lastName: "",
+});
+
+customForm.handleSubmit((values) => {
+  type test = Expect<
+    // Expect that inside handleSubmit, it's inferred as
+    // { firstName: string; lastName: string }
+    Extends<
+      {
+        firstName: string;
+        lastName: string;
+      },
+      typeof values
+    >
+  >;
+});
+
+// Expect that only the methods we want are exposed
+type test = Expect<
+  Equal<keyof typeof customForm, "register" | "handleSubmit" | "getValues">
+>;