<html>

<body>
  <center id="output">
    <button onclick="run()">Run</button>
    <p>Output:</p>
    </br>
  </center>
</body>

</html>
button {
    background: #ff4848;
    color: #c2ffd9;
}


// Here, this func returns a Promise which is resolved after ms milisecond.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));

async function run() {
  print('First');
  await sleep(1000);
  print('Second');
}




















function print(msg) {
  document.querySelector('#output').innerHTML += msg;
  document.querySelector('#output').innerHTML += '</br>';
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.