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/useLazyRef/useLazyRef.js

@@ -0,0 +1,19 @@
+'use client';
+
+import * as React from 'react';
+const UNINITIALIZED = {};
+
+/**
+ * A React.useRef() that is initialized lazily with a function. Note that it accepts an optional
+ * initialization argument, so the initialization function doesn't need to be an inline closure.
+ *
+ * @usage
+ *   const ref = useLazyRef(sortColumns, columns)
+ */
+export default function useLazyRef(init, initArg) {
+  const ref = React.useRef(UNINITIALIZED);
+  if (ref.current === UNINITIALIZED) {
+    ref.current = init(initArg);
+  }
+  return ref;
+}