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Difference between <script>, <script async>, and <script defer>?
pranav m
walmarteasy
1completed
27
Answer
<script>(default)- Blocks HTML parsing until script is loaded and executed.
- Slows rendering.
<script async>- Loads script asynchronously (parallel with HTML parsing).
- Executes as soon as it’s ready (may interrupt parsing).
- Best for independent scripts (ads, analytics).
<script defer>- Loads script asynchronously (like async).
- Executes after HTML is fully parsed, in order they appear.
- Best for scripts that depend on DOM.
Summary
Attribute | Load | Execute |
|---|---|---|
none | Blocking | Immediately (blocks parsing) |
async | Parallel | As soon as loaded (non-sequential) |
defer | Parallel | After parsing (sequential) |
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