Javascript asynchronous and synchronous function calls

async_and_sync.js

async function fetchData1() {
  // Simulate API 1 call (e.g., fetching data)
  await new Promise((resolve) => setTimeout(resolve, 1000));
  return 'Data from API 1';
}

async function fetchData2() {
  // Simulate API 2 call (e.g., fetching data)
  await new Promise((resolve) => setTimeout(resolve, 1500));
  return 'Data from API 2';
}

async function mainAsync() {
  const start = Date.now();
  const result1Promise = fetchData1();
  const result2Promise = fetchData2();
  const [result1, result2] = await Promise.all([result1Promise, result2Promise]);
  const end = Date.now();

  console.log('Result from API 1:', result1);
  console.log('Result from API 2:', result2);
  console.log('Total execution time (async):', end - start, 'ms');
}

function fetchData1Sync() {
  // Simulate API 1 call (e.g., fetching data)
  for (let i = 0; i < 1e7; i++) {} // Intentionally slow
  return 'Data from API 1';
}

function fetchData2Sync() {
  // Simulate API 2 call (e.g., fetching data)
  for (let i = 0; i < 2e7; i++) {} // Intentionally slower
  return 'Data from API 2';
}

function mainSync() {
  const start = Date.now();
  const result1 = fetchData1Sync();
  const result2 = fetchData2Sync();
  const end = Date.now();

  console.log('Result from API 1:', result1);
  console.log('Result from API 2:', result2);
  console.log('Total execution time (sync):', end - start, 'ms');
}

// calling functions asynchronously will take 1500 ms instead of timeout sum 1000+1500 = 2500 ms
mainAsync();

// calling functions synchronously
mainSync();