Answer
Both `async` and `defer` allow an external classic script to download while HTML parsing continues. • An async script executes as soon as it is ready, so multiple async scripts do not preserve document order. • A deferred script executes after parsing and deferred scripts preserve document order. • Module scripts are deferred by default unless `async` is specified.
💡 Simple Example
<script async src="/analytics.js"></script><script defer src="/app.js"></script>
⚡ Quick Revision
Use async for independent scripts and defer for ordered scripts that run after HTML parsing.