memoizeOnce.ts

const NO_ARGUMENTS_YET = Symbol("no arguments yet");

function allEqual<Arr extends any[]>(first: Arr, second: Arr): boolean {
  return first.every((value, i) => value === second[i]);
}

export function memoizeOnce<ArgsT extends any[], ReturnT>(
  fn: (...args: ArgsT) => ReturnT,
  comparator: (prevArgs: ArgsT, nextArgs: ArgsT) => boolean = allEqual
) {
  let lastCalledWithArgs: ArgsT | typeof NO_ARGUMENTS_YET = NO_ARGUMENTS_YET;
  let cachedResult: ReturnT;
  return (...args: ArgsT) => {
    if (
      lastCalledWithArgs !== NO_ARGUMENTS_YET &&
      comparator(lastCalledWithArgs, args)
    ) {
      return cachedResult;
    }

    lastCalledWithArgs = args;
    cachedResult = fn(...args);
    return cachedResult;
  };
}