async-practice.js

function main(callback1, callback2) {
  callback1();

  callback2();
  callback2();
  callback2();
}

function helloWorld() {
  console.log("hello world");
}

function helloTelkomsel() {
  console.log("hello telkomsel");
}

main(helloWorld, helloTelkomsel);

let array = [20, 21, 22, 23];

let i;

for (i = 0; i < array.length; i++) {
  console.log(i);
  setTimeout(function logElement() {
    console.log("index:", i);
    console.log("element:", array[i]);
  }, 5000);
  console.log("incrementing i");
}