Should you use async or defer for most scripts?
defer. It is non-blocking, executes in order, and runs after the DOM is ready. Use async only for independent scripts like analytics and ads.
Verify This Answer
Cross-check this information using these trusted sources:
More FAQs in async and defer Best Practices
In the <head>. This starts the download early (in parallel with HTML parsing) while deferring execution until after parsing. This is faster than placing scripts at the bottom of <body>.
Yes. <script type='module'> is automatically deferred. You do not need to add the defer attribute. The script downloads in parallel and executes after parsing.
No. async does not guarantee execution order. If script B depends on A, use defer for both. defer guarantees order.
Still have questions?
Browse all our FAQs or reach out to our support team