promise-all.ts

const simulateSlowHttpRequest = async (dummyData: string): Promise<string> =>
  new Promise<string>((resolve) => setTimeout(() => resolve(dummyData), 2000));

const bootstrap = async (): Promise<void> => {
  /**
   * Test A
   */
  const startA = Date.now();

  const aA = await simulateSlowHttpRequest('a');
  const aB = await simulateSlowHttpRequest('b');
  const aC = await simulateSlowHttpRequest('c');

  console.log(`Test A took ${Date.now() - startA}ms`, { aA, aB, aC });
  // ^ Test A took 6009ms { aA: 'a', aB: 'b', aC: 'c' }

  /**
   * Test B
   */
  const startB = Date.now();

  const [bA, bB, bC] = await Promise.all([
    simulateSlowHttpRequest('d'),
    simulateSlowHttpRequest('e'),
    simulateSlowHttpRequest('f'),
  ]);

  console.log(`Test B took ${Date.now() - startB}ms`, { bA, bB, bC });
  // ^ Test B took 2003ms { bA: 'd', bB: 'e', bC: 'f' }
};

bootstrap().catch((error: unknown) => {
  console.error(error);
  process.exit(1);
});