https://medium.com/javascript-in-plain-english/understand-javascript-sequencing-and-asynchronous-behaviors-to-leverage-code-parallelism-1e381fa8d33c

async-vs-sync-loop.js

const chalk = require("chalk").default;

// Fail after time
function ApiError(time, theme) {
  return new Promise((_, reject) => {
    setTimeout(() => {
      reject("=> API call " + chalk.red("failed") + " with [" + chalk.blue(theme) + "] at " + time);
    }, time);
  });
}

// Block execution and succeed after time
function createFile(time, theme) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve("=> Created file for [" + chalk.blue(theme) + "]");
    }, time);
  });
}

// Succeed after time
function ApiSuccess(time, theme) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve("=> Succeed API call on [" + chalk.blue(theme) + "]");
    }, time);
  });
}

// Loop occurence
async function loopOccurence(currentTheme) {
  const loopJobName = chalk.green("✅ Finished job [" + chalk.blue(currentTheme) + "] at");

  // Starting timer for counting duration of loop
  console.time(loopJobName);

  try {
    console.log(`=> API call [${chalk.blue(currentTheme)}] is started`);

    // To make some task fails and some work 50% chances.
    const randomBooleanTrue = Math.random() >= 0.5;

    if (randomBooleanTrue) {
      await ApiError(3000, currentTheme);
    } else {
      const result = await ApiSuccess(3000, currentTheme);
      console.log(result);
    }

    // If API succeeded, create file action
    const writeOperationResult = await createFile(2000, currentTheme);
    console.log(writeOperationResult);

    // End timer
    console.timeEnd(loopJobName);
  } catch (error) {
    console.log(error);

    // End timer
    console.timeEnd(loopJobName);
  }
}

(async () => {
  try {
    const programExecutionTimer = chalk.green("✅ Reached end of script time");

    const themes = ["sport", "cooking", "education"];

    // Starting timer for script execution duration
    console.time(programExecutionTimer);
    console.log(chalk.blueBright("🚀 Starting synchronous script execution"));

    // 1st case : Synchronous loop that wait at each occurence
    for (let currentTheme of themes) {
      await loopOccurence(currentTheme);
    }

    // 2nd case: asynchronous loop that use parallelism
    // for (let currentTheme of themes) {
    //   loopOccurence(currentTheme);
    // }

    // 3rd case: asynchronous loop that use parallelism using functional programming
    // themes.forEach(loopOccurence);

    // 4th case: Even better and most efficient way
    // await Promise.all(themes.map(loopOccurence));

    // End timer for script execution duration
    console.timeEnd(programExecutionTimer);
  } catch (error) {
    console.log(error);
  }
})();