add docs

README.md

@@ -97,6 +97,36 @@ const AddressSubform: FC<{field: FormBuilder<Address>}> = ({field}) => {
 }
 ```
 
+## Field arrays
+
+Fields which are typed as arrays provide a `$useFieldArray()` hook which can be used to map over the contents, as well
+as mutate them using operations such as `append`, `insert`, `move` and `remove`.
+
+The `fields` returned by `$useFieldArray` are themselves `FormBuilder`s that can be registered on inputs or passed to
+other Subform components.
+
+```tsx
+import { FC } from "react";
+
+const AddressesSubform: FC<{field: FormBuilder<Person[]>}> = ({field}) => {
+    const {fields, append} = field.$useFieldArray();
+    const add = () => {
+        append({state: '', city: '', /* etc. */});
+    }
+    return <div>
+        {fields.map(f => <AddressSubForm key={f.$key} field={f} />)}
+        <button onClick={add}>Add new address</button>
+    <div>
+}
+```
+
+The `$key` contains a unique id for the array item and must be passed as the `key` when [rendering the list](https://react.dev/learn/rendering-lists).
+
+Note: Field arrays are intended for use with arrays of objects. When dealing with arrays of primitives, you can either
+wrap the primitive in an object, or use a controller (`$useController`) to implement your own array logic.
+
+For more information, see the React Hook Form docs on [`useFieldArray`](https://react-hook-form.com/docs/usefieldarray).
+
 ## Compatibility with `useForm`
 
 Currently, `useFormBuilder` is almost compatible with `useForm`. This means you get the entire bag of tools provided by
@@ -107,4 +137,4 @@ streamline this API and increase its type-safety.
 
 ## License
 
-MIT
+MIT

src/formbuilder.test.tsx

@@ -66,7 +66,7 @@ describe("useFormBuilder", () => {
     list: [
       { id: "0", action: "frobnicate" },
       { id: "1", action: "skedaddle" },
-    ]
+    ],
   };
 
   beforeAll(() => {
@@ -159,7 +159,10 @@ describe("useFormBuilder", () => {
 
     await waitFor(() => {
       expect(watchedRoot).toHaveTextContent(
-        JSON.stringify({...defaultValues, person: {...defaultValues.person, firstName: "Joe"}})
+        JSON.stringify({
+          ...defaultValues,
+          person: { ...defaultValues.person, firstName: "Joe" },
+        })
       );
       expect(watchedRoot).toHaveTextContent("Smith");
       expect(watchedFirstName).toHaveTextContent("Joe");
@@ -231,17 +234,17 @@ describe("useFormBuilder", () => {
     const harness = createHarness({ defaultValues }, (builder) => {
       const { fields } = builder.fields.list.$useFieldArray();
 
-      return <div>
-        {
-          fields.map((field, i) => (
+      return (
+        <div>
+          {fields.map((field, i) => (
             <input
               key={field.$key}
               {...field.action()}
               aria-label={`action-${i}`}
             />
-          ))
-        }
-      </div>
+          ))}
+        </div>
+      );
     });
 
     render(<harness.Form />);
@@ -250,5 +253,5 @@ describe("useFormBuilder", () => {
       expect(screen.getByLabelText("action-0")).toHaveValue("frobnicate");
       expect(screen.getByLabelText("action-1")).toHaveValue("skedaddle");
     });
-  })
+  });
 });