Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/node_modules/@mui/utils/useOnMount/useOnMount.js

@@ -0,0 +1,13 @@
+'use client';
+
+import * as React from 'react';
+const EMPTY = [];
+
+/**
+ * A React.useEffect equivalent that runs once, when the component is mounted.
+ */
+export default function useOnMount(fn) {
+  /* eslint-disable react-hooks/exhaustive-deps */
+  React.useEffect(fn, EMPTY);
+  /* eslint-enable react-hooks/exhaustive-deps */
+}