callback-promise-async.js

//asynchronous
function logWord(word) {
  setTimeout(
    function() {
      console.log(word);
    },
    Math.floor(Math.random() * 100) + 1
    // return value between 1 ~ 100
  );
}

function logAll() {
  logWord("A");
  logWord("B");
  logWord("C");
}
logAll();

Callbacks;
function logWord(word, callback) {
  setTimeout(function() {
    console.log(word);
    callback();
  }),
    Math.floor(Math.random() * 100) + 1;
}

function logAll() {
  logWord("A", function() {
    logWord("B", function() {
      logWord("C", function() {});
    });
  });
}
logAll();

// Promises
function logWord(word) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log(word);
      resolve();
    }, Math.floor(Math.random() * 100) + 1);
  });
}

function logAll() {
  logWord("A")
    .then(function() {
      return logWord("B");
    })
    .then(function() {
      return logWord("C");
    });
}

logAll();

//ansyc-await syntactic sugar
async function logAll() {
  await logWord("A");
  await logWord("B");
  await logWord("C");
}

logAll();