Can you mix async and defer on the same page?
Yes. Use async for independent scripts (analytics, ads) and defer for dependent scripts (app logic). They do not interfere with each other. async scripts may run before or after deferred scripts.
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More FAQs in async and defer: Real-World Examples
<script src='react.js' defer></script><script src='react-dom.js' defer></script><script src='app.js' defer></script>. All deferred: download in parallel, execute in order (react first, app last).
<script src='analytics.js' async></script>. Analytics is independent (does not depend on other scripts or the DOM), so async is appropriate. It loads and runs whenever it is ready.
The dependency may not be loaded when the script executes. async does not guarantee order. Use defer for both scripts to guarantee the dependency loads first.
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