Created a cached version of any function with a single argument.

cachify.ts

/**
 * Create a cached version of a function.
 *
 * @example cachedCalcArea = cachify(calcArea);
 * @param fn Function whose results you want to cache
 * @see TypeScript version of https://dev.to/kepta/javascript-underdogs-part-1---the-weakmap-4jih
 */
export const cachify = <T extends object, R>(fn: (arg: T) => R) => {
  const cache = new WeakMap(); // Use Map() when dealing with non-object arguments
  return (arg: T) => {
    if (cache.has(arg)) {
      return cache.get(arg);
    }
    const computed = fn(arg);
    cache.set(arg, computed);
    return computed;
  };
};