async function sayHello() {
  return 'Hello World';
}

sayHello().then((value) => console.log(value));

If we just had function sayHello(), then `then` doesn't make sense.

async function sayHi() {
  return 'Hi';
}

async function sayHello(arg = 1) {
  console.log('in say hello');
  if (arg === 1) {
    const inner = await sayHi();
    return inner;
  } else {
    return 'Hello Worlds';
  }
}

sayHello().then((value) => console.log(value));;

- Will wait for 'hi'

doSomething(param1, param2, function(err, paramx) {
  doMore(paramx, function(err, result) {
    insertRow(result function(err) {
      yetAnotherOperation(someparameter, function(s) {
        somethingElse(function(x) {
          // ...
        });
      });
    });
  });
});

function something() {
  return doSomething(param1, param2);
}

function main() {
  something().then((err, paramx) => {
    doMore(paramx).then((err, result) => {
      insertRow(result).then((err) => {
        // ...
      });
    });
  });
}