Should you use async for scripts with dependencies?
No. async does not guarantee execution order. If script B depends on A, use defer for both. defer guarantees order.
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More FAQs in async and defer Best Practices
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.
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.
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