onion-core/src/frontend/use_const.ts

import * as React from "react";

// Why doesn't React have this functionality built-in? (and implemented more efficiently than hacking with useRef)
export function useConst<T>(initialCb: ()=>T): T {
  const ref = React.useRef<T>();
  if (ref.current === undefined) {
    const initialValue = initialCb();
    ref.current = initialValue;
  }
  return ref.current!;
}