What is the difference between async and defer (Ola question)?
async downloads in parallel and executes as soon as ready (unordered, briefly blocks parsing). defer downloads in parallel and executes after HTML parsing (ordered, non-blocking).
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More FAQs in async and defer Interview Questions (Ola)
No. async scripts execute in whatever order they finish downloading. If a later script downloads first, it executes first. Use defer if order matters.
Yes. defer scripts execute in the order they appear in the HTML, after all HTML parsing is complete. This makes defer safe for scripts with dependencies.
The script blocks HTML parsing and rendering. The browser stops parsing, downloads the script, executes it, then resumes parsing. This makes the page feel slow.
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