Answer
Both `defer` and `async` download a script without stopping HTML download. • `async` runs as soon as ready, so order is not guaranteed. • `defer` waits for HTML parsing and keeps script order. • Choose the option whose defined semantics and behavior match the task.
💡 Simple Example
<script defer src="app.js"></script>
⚡ Quick Revision
Use defer for ordered page scripts; async suits independent scripts.