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65 lines
2.6 KiB
65 lines
2.6 KiB
Performance
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==
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## Glossary
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- **Critical Rendering Path** -
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- `requestAnimationFrame`
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## General Strategies
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1. Minimize Bytes.
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1. Reduce critical resources.
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1. Reduce CRP length. TODO: Explain what CRP length is.
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## Loading
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- Minify, Compress, Cache assets.
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- Browsers have a [preloader](https://andydavies.me/blog/2013/10/22/how-the-browser-pre-loader-makes-pages-load-faster/) to load assets ahead of time.
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## Rendering
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- Remove whitespace and comments from HTML/CSS/JS file via minification.
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- CSS
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- CSS blocks rendering AND JavaScript execution.
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- Split up CSS for fewer rendering blocking CSS stylesheets by using media attributes.
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- Download only the necessary CSS before the browser can start to render.
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- https://developers.google.com/web/fundamentals/design-and-ui/responsive/#css-media-queries
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- Use Simpler selectors.
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- JavaScript
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- JS blocks HTML parsing. If the script is external, it will have to be downloaded first. This incurs latency in network and execution.
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- Shift `<script>` tags to the bottom.
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- Async:
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- Scripts that don't modify the DOM or CSSOM can use the `async` attribute to tell the browser not to block DOM parsing and does not need to wait for the CSSOM to be ready.
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- Defer JavaScript execution:
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- There is also a `defer` attribute available. The difference is that with `defer`, the script waits to execute until after the document has been parsed, whereas `async` lets the script run in the background while the document is being parsed.
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- Use web workers for long running operations to move into a web worker thread.
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- Use `requestAnimationFrame`
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###### References
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- https://bitsofco.de/understanding-the-critical-rendering-path/
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## Measuring
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- [Navigation Timing API](https://developer.mozilla.org/en/docs/Web/API/Navigation_timing_API) is a JavaScript API for accurately measuring performance on the web. The API provides a simple way to get accurate and detailed timing statistics natively for page navigation and load events.
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- `performance.timing`: An object with the timestamps of the various events on the page. Some uses:
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- Network latency: `responseEnd` - `fetchStart`.
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- The time taken for page load once the page is received from the server: `loadEventEnd` - `responseEnd`.
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- The whole process of navigation and page load: `loadEventEnd` - `navigationStart`.
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## Tools
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- Yahoo YSlow
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- Google PageSpeed Insights
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- WebPageTest
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- Sitespeed.io
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- Google Lighthouse
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## Web Performance Rules
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- https://www.html5rocks.com/en/tutorials/webperformance/basics/
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- http://stevesouders.com/hpws/rules.php
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- https://developer.yahoo.com/performance/rules.html
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- https://browserdiet.com/en/
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