According to this image by default HTML parsing should pause when it encounters an external and wait until the script is downloaded and executed before continuing.
I've been testing this and I can't replicate this logic.
I've put in a few sample request after my initial request with no async tag but they all seem to be requested simultaneously
<!DOCTYPE html>
<html lang="en">
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<title>Testing</title>
<script src="https://code.highcharts.com/highcharts.js"></script>
</head>
<body>
<div id="root"></div>
<img
src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQReLvoUiu3NJ_g63RtEws3IN9N7fGp6dHRDEirrJEIZ9wW4LED"
/>
</body>
</html>
I would expect from what I've read that the second highcharts request wouldn't be initiated until the first script has been fetched and executed due to HTML parsing being paused. On Chrome 75. Does chrome async by default?