JSFiddle - React, Tailwind, and code Playground

JavaScript

const array = [1, 2, 3];

for (let i = 0; i < array.length; i++) {
  console.log(array[i]);
}

for (const itemOfArray of array) {
  console.log(itemOfArray);
}

for (const itemInArray in array) {
  console.log(itemInArray);
}


const brothers = {
  id1: {name: "SĂ©bastien", age: 34},
  id2: {name: "Antoine", age: 23}
};

function incrementBrothersAges() {
  return Object.entries(brothers)
  .reduce((acc,[id,brother]) => {
   acc[id] = {...brother,age: brother.age + 1};
   return acc;  
  },{})
}

console.log("incrementBrothersAges",incrementBrothersAges())



async function runCountryTask(country) {

  const taskDuration = Math.random() * 2000;
  await new Promise(resolve => setTimeout(resolve, taskDuration))
  
  console.log(`Task complete for ${country}, duration=${taskDuration}`)
 
}

async function forEachAsyncSequential(array,asyncFn) {
  for (const item of array) {
    await asyncFn(item);
  }
}

async function forEachAsyncSequential2(array,asyncFn) {
  await array.reduce((acc,item) => {
    return acc.then(() => asyncFn(item))
  },Promise.resolve());
}

async function runAllCountryTasks() {
  const countries = ["FR","EN","US","DE","UK","IT"];
  await Promise.all(countries.map(runCountryTask))
  console.log("\n");
  await forEachAsyncSequential(countries,runCountryTask);
  console.log("\n");
  await forEachAsyncSequential2(countries,runCountryTask);
  console.log("\n");
}



runAllCountryTasks();