async-call.js

function wait(ms) {
  var start = Date.now();
  var now = start;
  while (now - start < ms) {
    now = Date.now();
  }
}

function drink(person, coffee) {
  console.log(person + '는 <' + coffee + '>를 마십니다');
}

function orderCoffeeSync(menu) {
  console.log(menu + '가 접수되었습니다');
  wait(2000);
  return '코드벅스 ' + menu;
}

function orderCoffeeAsync(menu, callback) {
  console.log(menu + '가 접수되었습니다');
  setTimeout(function() {
    callback('코드벅스 ' + menu);
  }, 2000);
}


let customers = [{
  name: 'steve',
  whatIwant: '카페라떼'
}, {
  name: 'johnny',
  whatIwant: '아메리카노'
}];

// call synchronously
customers.forEach(function(customer) {
  let coffee = orderCoffeeSync(customer.whatIwant);
  drink(customer.name, coffee);
});

// call asynchronously
customers.forEach(function(customer) {
  orderCoffeeAsync(customer.whatIwant, function(coffee) {
    drink(customer.name, coffee)
  });
});