Async/Await Syntax

async function sequentialMap(array, asyncFn) {
  const results = [];
  for (const item of array) {
    results.push(await asyncFn(item));
  }
  return results;
}

async function concurrentMap(array, asyncFn, concurrency = 3) {
  const results = new Array(array.length);
  const executing = new Set();
  
  async function execute(index) {
    const item = array[index];
    executing.add(index);
    try {
      results[index] = await asyncFn(item);
    } finally {
      executing.delete(index);
    }
  }
  
  let index = 0;
  while (index < array.length) {
    if (executing.size < concurrency) {
      execute(index++);
    } else {
      await Promise.race(Array.from(executing).map(
        i => results[i]
      ));
    }
  }
  
  return results;
}