[Doc] Improve FunctionField documentation

docs/FunctionField.md

@@ -5,22 +5,122 @@ title: "The FunctionField Component"
 
 # `<FunctionField>`
 
-If you need a special function to render a field, `<FunctionField>` is the perfect match. It passes the `record` to a `render` function supplied by the developer. For instance, to display the full name of a `user` record based on `first_name` and `last_name` properties:
+If you need a special function to render a field, `<FunctionField>` is the perfect match. It executes a `render` function using the current record as parameter.
+
+<iframe src="https://www.youtube-nocookie.com/embed/gcgefw79QdM" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen style="aspect-ratio: 16 / 9;width:100%;margin-bottom:1em;"></iframe>
+
+## Usage
+
+`<FunctionField>` requires a `render` prop, which is a function that takes the current record as argument and returns a string or an element.
+
+For instance, to display the full name of a `user` record based on `first_name` and `last_name` properties:
 
 ```jsx
-import { FunctionField } from 'react-admin';
+import { List, Datagrid, FunctionField } from 'react-admin';
 
-<FunctionField label="Name" render={record => `${record.first_name} ${record.last_name}`} />
+const UserList = () => (
+    <List>
+        <Datagrid>
+            <FunctionField
+                source="last_name"
+                render={record => `${record.first_name} ${record.last_name}`}
+            />
+            ...
+        </Datagrid>
+    </List>
+);
 ```
 
-## Properties
+Theoretically, you can omit the `source` for the `<FunctionField>` since you provide the render function. However, when used inside a `<Datagrid>`, providing the `source` prop (or the `sortBy` prop) is required to make the column sortable. When a user clicks on a column, `<Datagrid>` uses these properties to sort the data.
+
+`<FunctionField>` is based on [the `useRecordContext` hook](./useRecordContext.md).
+
+## Props
 
 | Prop     | Required | Type     | Default | Description                                                                |
 | -------- | -------- | -------- | ------- | -------------------------------------------------------------------------- |
 | `render` | Required | function | -       | A function returning a string (or an element) to display based on a record |
 
 `<FunctionField>` also accepts the [common field props](./Fields.md#common-field-props).
 
-**Tip**: Technically, you can omit the `source` and `sortBy` properties for the `<FunctionField>` since you provide the render function. However, providing a `source` or a `sortBy` will allow the `Datagrid` to make the column sortable, since when a user clicks on a column, the `Datagrid` uses these properties to sort. Should you provide both, `sortBy` will override `source` for sorting the column.
+## `render`
+
+The `render` prop accepts a function that takes the current record as argument and returns a string or an element.
+
+```tsx
+// return a string
+const render = (record: any) => `${record.first_name} ${record.last_name}`;
+
+// return an element
+const render = (record: any) => (
+    <>{record.first_name} <strong>{record.last_name}</strong></>
+);
+```
+
+React-admin wraps the result of the `render` function in a `<Typography>` component.
+
+Since this function executes in a [RecordContext](./useRecordContext.md), you can even use other Field components to compute the value:
+
+```tsx
+import { List, Datagrid, FunctionField, TextField } from 'react-admin';
+
+const render = () => (
+    <span>
+        <TextField source="first_name" />{' '}
+        <TextField source="last_name" />
+    </span>
+);
+const UserList = () => (
+    <List>
+        <Datagrid>
+            <FunctionField source="last_name" label="Name" render={render} />
+            ...
+        </Datagrid>
+    </List>
+);
+```
+
+However, if you only need to combine Field components, prefer [the `<WrapperField>` component](./WrapperField.md) for a simpler syntax:
+
+```tsx
+import { List, Datagrid, WrapperField, TextField } from 'react-admin';
+
+const UserList = () => (
+    <List>
+        <Datagrid>
+            <WrapperField label="Name" source="last_name">
+                <TextField source="first_name" />
+                <TextField source="last_name" />
+            </WrapperField>
+            ...
+        </Datagrid>
+    </List>
+);
+```
+
+## TypeScript
+
+To type the `record` argument of the `render` function, provide the record's type as a generic parameter to the component:
+
+```tsx
+import { List, Datagrid, FunctionField } from 'react-admin';
+
+interface User {
+    id: number;
+    first_name: string;
+    last_name: string;
+}
 
-**Tip**: If you want to combine two existing Field components, check  [the `<WrapperField>` component](./WrapperField.md) instead.
+const UserList = () => (
+    <List>
+        <Datagrid>
+            <FunctionField<User>
+                source="last_name"
+                label="Name"
+                render={record => `${record.first_name} ${record.last_name}`}
+            />
+            ...
+        </Datagrid>
+    </List>
+);
+```

docs/WrapperField.md

@@ -7,6 +7,8 @@ title: "The WrapperField Component"
 
 This component simply renders its children. Why would you want to use such a dumb component? To combine several fields in a single cell (in a `<Datagrid>`), in a single row (in a `<SimpleShowLayout>`) or in a group of inputs (in a `<SimpleFormConfigurable>`) .
 
+## Usage
+
 `<WrapperField>` allows to define the `label` and sort field for a combination of fields:
 
 ```jsx
@@ -44,5 +46,8 @@ const PostEdit = () => (
 );
 ```
 
+**Tip**: If you just want to combine two fields in a string, check  [the `<FunctionField>` component](./FunctionField.md) instead.
+
+## Props
 
-**Tip**: If you just want to combine two fields in a string, check  [the `<FunctionField>` component](./FunctionField.md) instead.
+`<WrapperField>` accepts the [common field props](./Fields.md#common-field-props).