Page speed Standard Understanding

PageSpeed

• Understanding Lab vs Field Data

  • Lab Data

  • Field Data

• Lighthouse performance scoring Lighthouse performance scoring  |  Chrome for Developers → Using HTTPArchive

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• User-centric performance metrics User-centric performance metrics  |  Articles  |  web.dev
  
  

Browser Life Cycle Community | DigitalOcean

The critical rendering path https://medium.com/@luisvieira_gmr/understanding-the-critical-rendering-path-rendering-pages-in-1-second-735c6e45b47a

• DOM

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• CSSOM

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• Render Tree

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• Layout → Paint
  
  

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• Dealing with Javascript
  
  

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• Parser blocking vs render blocking

  • If there is any inline <script> under an external CSS's <link> tag, even if that is just an empty <script> tag that contains no JavaScript at all, the DOM construction for the HTML below that <script> tag will still be blocked util the external CSS is fetched. If you have a slow network connection, that empty <script> still causes a long delay of DOM construction. Because the <script> tag waits for the external CSS, and DOM construction waits for the script. In this case the external CSS resource implicitly causes a parser-blocking.
    
    

• Make sure no critical requests are redirected.

 How to Prioritise Requests The Critical Request: How to Prioritise Requests to Improve Speed

async vs defer

Resource Hints : preload, preconnect, prefetch