--- name: thedaviddias/defer-async source: https://app.decimal.ai/s/thedaviddias-defer-async@1/SKILL.md source_sha256: 2018bf80c240 --- # Load scripts with defer, async, or type=module A plain <script> tag in the document head blocks all HTML parsing until the script downloads, parses, and executes. On a slow network this can add seconds of white-screen time before any content renders. defer and async allow the browser to continue parsing HTML while the script downloads, reducing Time to First Contentful Paint dramatically. ## Quick Reference - defer downloads in parallel and executes after HTML parsing, in order — use for most scripts - async downloads in parallel and executes immediately when ready — use for independent scripts - type=module always defers and enables ES module syntax - Never place scripts in without defer or async ## Check Find all script tags in this HTML file. Flag any in the without defer or async, and any at the bottom of that could be in with defer. ## Fix Add defer or async to script tags in the document head, or convert to type=module where ES modules are used. ## Explain Explain the difference between defer, async, and type=module script loading, and when to use each. ## Code Review Review templates, server-rendered HTML, and shared components that output markup related to Load scripts with defer, async, or type=module. Flag exact elements, attributes, and routes where the rendered HTML violates the rule. --- For full implementation details, code examples, and framework-specific guidance, see `references/rule.md`. Rule page: https://frontendchecklist.io/en/rules/html/defer-async