68 lines
2.3 KiB
Markdown
68 lines
2.3 KiB
Markdown
# Web Performance Checklist
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A checklist to make sure you website will be fast!
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## HTML
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* critical link tags are in head
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* less critical link tags are end of body
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* less critical link tags lazy load
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* `<link rel="preload" as="style" onload="this.rel='stylesheet'" id='dashicons-css' `
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* JS loads with the async property
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* `<script async src="https://hi.js"></script>`
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* or `defer` when scripts have dependencies
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## Fonts
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* Fonts should always load `woff2` first
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* `woff` for fallback
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* You can use `font-display: swap;` to allow the browser to use a fallback font while custom font files are being downloaded.
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* eot, or truetype is only needed for `IE < 10`
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## CSS
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* Avoid expensive selectors when possible
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* `border-radius`
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* `box-shadow`
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* `transform`
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* `filter`
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* `:nth-child`
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* `position: fixed;`
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* Partial matching: `[class^="wrap"]`
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* Don't use universal selectors
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* Universal selectors like `*, [disabled], [type=“text”]`, etc. are very expensive for the browser to match, as every element in the DOM must be checked.
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* Avoid deeply nested dependent selectors
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* The descendant selector is very costly, as the browser must check for a match with every descendant element. On a complex web page, this can result in thousands and thousands (perhaps even more) of descendant selector searches.
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* Use media queries to load files based on use case
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```css
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<link href="style.css" rel="stylesheet" media="all">
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<link href="portrait.css" rel="stylesheet" media="orientation:portrait">
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<link href="print.css" rel="stylesheet" media="print">
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<link href="desktop.css" rel="stylesheet" media="(min-width: 720px)">
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```
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## JS
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* Bundles should always be minified
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* Bundles should have 0 comments, and all license text extracted to a separate file
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## Assets
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* All assets should be fingerprinted
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* All assets should have `Cache-Control: max-age=365000000, immutable` as a header
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* Assets should be served over http/2
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* Assets should only be served on a cookieless domain
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* All files should be cached by a CDN
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* Support Brotli compression
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* 15-30% smaller than gzip
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* Compress with gzip, or zopfli as a fallback to brotli
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*
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## PWA
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* Use a service worker to cache assets
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* Use a service worker to prefetch pages users will most likely navigate to next
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* Support offline, and spotty networks
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