Add note to node-loader on how to use w/ react 18

packages/node-loader/lib/index.js

@@ -3,8 +3,8 @@
  *
  * @typedef LoaderOptions
  * @property {boolean} [fixRuntimeWithoutExportMap=true]
- *   Several JSX runtimes, notably React and Emotion, don’t yet have a proper
- *   export map set up.
+ *   Several JSX runtimes, notably React below 18 and Emotion below 11.10.0,
+ *   don’t yet have a proper export map set up.
  *   Export maps are needed to map `xxx/jsx-runtime` to an actual file in ESM.
  *   This option fixes React et al by turning those into `xxx/jsx-runtime.js`.
  *

packages/node-loader/readme.md

@@ -105,9 +105,24 @@ It also exports the following identifier: `createLoader`.
 
 Create a Node ESM loader to compile MDX to JS.
 
-###### `options`
+##### `options`
 
 `options` are the same as [`compile` from `@mdx-js/mdx`][options].
+One extra field is supported:
+
+###### `options.fixRuntimeWithoutExportMap`
+
+Fix broken export maps (`boolean`, default: `true`).
+
+Several JSX runtimes, notably React below 18 and Emotion below 11.10.0, don’t
+have a proper export map set up.
+Export maps are needed to map `xxx/jsx-runtime` to an actual file in ESM.
+This option fixes React et al by turning those into `xxx/jsx-runtime.js`.
+
+> 👉 **Note**: If you are using recent React, or other proper packages, you
+> have to turn this field off.
+> See the example below on how to configure your loader.
+> Pass `fixRuntimeWithoutExportMap: false` in options to it.
 
 ###### Example
 
@@ -122,7 +137,7 @@ const {load, getFormat, transformSource} = createLoader(/* Options… */)
 export {load, getFormat, transformSource}
 ```
 
-This example can then be used with `node --experimental-loader=my-loader.js`.
+This example can then be used with `node --experimental-loader=./my-loader.js`.
 
 Node itself does not yet support multiple loaders but it is possible to combine
 multiple loaders with [`@node-loader/core`][node-loader-core].