cache of an async function

async-cache.js

const resultMap: Map<string, any> = new Map();
const loadData = async (loader: Function, ...args: any) => {
  // is there a better way...
  const key = JSON.stringify(args);

  if (resultMap.has(key)) {
    const val = resultMap.get(key);
    if (val.state === 'loading') {
      return await val.promise();
    } else if (val.state === 'failed') {
      throw val.error;
    } else {
      return val.result;
    }
  }

  const resolves: Function[] = [];
  const rejects: Function[] = [];
  const promise = () => {
    return new Promise((resolve, reject) => {
      resolves.push(resolve);
      rejects.push(resolve);
    });
  }

  resultMap.set(key, {state: 'loading', promise});
  try {
    const result = await loader(...args);
    resultMap.set(key, {state: 'loaded', result});
    resolves.forEach(resolve => resolve(result));
    return result;
  } catch(error) {
    resultMap.set(key, {state: 'failed', error});
    rejects.forEach(reject => reject(error));
    throw error;
  }
};