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https://github.com/danilqa/web-performance-handbook

📖 Selected and essential information on web performance collected in one place.
https://github.com/danilqa/web-performance-handbook

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📖 Selected and essential information on web performance collected in one place.

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README 

          
# Web Performance Handbook






This handbook helps to quickly understand the topic and start improving performance. It contains a metrics glossary, 

a compilation of useful tools, and a catalog of necessary materials. 



I really want to share proven knowledge to make the web even better and faster. Support and bookmark the project by giving it a star! ⭐



## Table of Contents



- [Web Performance Handbook](#web-performance-handbook)

  - [Table of Contents](#table-of-contents)

  - [Tools](#tools)

    - [Global Stats](#global-stats)

    - [Treo — Site Speed](#treo--site-speed)

    - [Web Vitals (extension)](#web-vitals-extension)

    - [PageSpeed Insights](#pagespeed-insights)

    - [WebPageTest](#webpagetest)

    - [Lighthouse](#lighthouse)

    - [DevTools Performance (with experimental features)](#devtools-performance-with-experimental-features)

  - [Monitoring](#monitoring)

    - [LHCI Server (open-source)](#lhci-server-open-source)

    - [DebugBear (paid)](#debugbear-paid)

  - [Optimizing Hydration](#optimizing-hydration)

      - [Disable Hydration](#disable-hydration)

      - [Server Components](#server-components)

  - [Optimizing Page Load Speed](#optimizing-page-load-speed)

    - [Image Proxy: Use avif / webp / progressive jpeg](#image-proxy-use-avif--webp--progressive-jpeg)

    - [Data Compression with brotli](#data-compression-with-brotli)

  - [Optimizing Bundle](#optimizing-bundle)

    - [Tools to Analyze](#tools-to-analyze)

      - [Statoscope](#statoscope)

      - [Bundle Analyzer](#bundle-analyzer)

      - [Why?](#why)

    - [Webpack Alias: Remove 3-rd Party Code from Bundle](#webpack-alias-remove-3-rd-party-code-from-bundle)

    - [Lazy Code Loading: On Viewport, on Interaction](#lazy-code-loading-on-viewport-on-interaction)

    - [Deduplication](#deduplication)

    - [Webpack: Magic Comments on Imports](#webpack-magic-comments-on-imports)

  - [React Tools](#react-tools)

    - [Why Did You Render](#why-did-you-render)

    - [React DevTools Profiler](#react-devtools-profiler)

  - [Learning Resources](#learning-resources)

    - [Browser Rendering Optimization Course](#browser-rendering-optimization-course)

    - [Web App Performance Course](#web-app-performance-course)

  - [Metrics](#metrics)

    - [CLS](#cls)

    - [DCL](#dcl)

    - [FCP](#fcp)

    - [FID](#fid)

    - [FP](#fp)

    - [INP](#inp)

    - [L](#l)

    - [LCP](#lcp)

    - [SI](#si)

    - [TBT](#tbt)

    - [TTI](#tti)

    - [TTFB](#ttfb)



---



## Tools



### Global Stats



Browser market share worldwide. This allows you to see device and browser usage in specific regions.



[link](https://gs.statcounter.com/browser-market-share/)



### Treo — Site Speed



How to view historical performance data of real users?



Allows viewing annual reports for websites based on Light House and CrUX (Chrome User Experience Report) metrics. 

Filters can also be set, such as internet connection speed, location, and device. Uses real user data. Very useful for observing trends 

and metrics specific to certain user types.



[link](https://treo.sh/sitespeed)



### Web Vitals (extension)



Collect metrics such as [**INP**](#INP), [LCP](#LCP), [CLS](#CLS), [FIP](#FIP), [FCP](#FCP), and [TTFB](#TTFB) in real-time and easily view them in a popup. 

Enabling logging in options can assist in debugging [INP](#INP).



[link](https://chrome.google.com/webstore/detail/web-vitals/ahfhijdlegdabablpippeagghigmibma/)



### PageSpeed Insights



Allows you to conduct Lighthouse performance tests remotely, in a more realistic environment. Can be used for taking 

more objective measurements, as computer powers vary among teammates. Especially, developers tend to have significantly 

more powerful computers than the general market. Also, for popular websites, it provides data from the CrUX report.



[link](https://pagespeed.web.dev)



### WebPageTest



The same as previous, but on steroids. Allows you to set up a testing environment: location, browser, its available 

functionality, connection speed, etc. Can record a video of the loading process, providing more understandable and 

detailed reports on the webpage loading process and requests.



[link](https://www.webpagetest.org/)



### Lighthouse



A tool designed for assessing the quality of a web page, focusing on core vitals metrics, SEO, and accessibility.

It is built into Chrome DevTools and can be also used as a CLI tool, making it especially useful for measuring 

performance during CI processes. Additionally, it offers practical suggestions to enhance the quality and loading 

speed of the page.



### DevTools Performance (with experimental features)



Record and analyze the performance of a page. It allows you to see the loading process in detail, including the

loading, scripting, rendering, and painting phases. It also provides a timeline of events, which can be used to

understand what is happening under the hood. For instance, you can see how long the hydration takes.



Hint:\

Enable the experimental "timeline-*" features in DevTools settings to see more information about events. It's especially 

useful for React apps. By default, it's challenging to understand what's really happening because of tons of anonymous

events.



---



## Monitoring



### LHCI Server (open-source)



Allows you to store historical performance data and see differences between builds. It integrates with CI/CD processes.



[GitHub link](https://github.com/GoogleChrome/lighthouse-ci/blob/main/docs/server.md)



### DebugBear (paid)



A tool for monitoring web performance and Lighthouse metrics. It can be used to set up alerts for performance regressions.



[link](https://www.debugbear.com/)



---



## Optimizing Hydration



#### Disable Hydration



React has a trick that allows you to disable hydration for a component. The server will render it once, then send an HTML that won't be hydrated. Perfect for static content.



```jsx



```



It's also available as part of an npm package:

[react-lazy-hydration](https://www.npmjs.com/package/react-lazy-hydration)



#### Server Components



[more them](https://nextjs.org/docs/app/building-your-application/rendering/server-components)



---



## Optimizing Page Load Speed



### Image Proxy: Use avif / webp / progressive jpeg



To improve LCP and reduce traffic volume, you can use image proxies or CDNs. They will reformat, resize, and optimize your images on the fly, and cache them immediately.



Possible solutions:

1. Cloudflare Images

2. UploadCare

3. [ImageProxy](https://github.com/imgproxy/imgproxy)

4. Implement manually: [Good starting point](https://github.com/Danilqa/image-proxy-service).



### Data Compression with brotli



Reduce the size of static files by 15-17% (the exact number is better to calculate using your own resources). The best results can be achieved using brotli with compression level 11. However, the compression time is longer than with gzip (level 9), so it's better to avoid using it on-the-fly and only use pre-compressed or cached versions.



[Comparison table](https://cran.r-project.org/web/packages/brotli/vignettes/brotli-2015-09-22.pdf)



---



## Optimizing Bundle



### Tools to Analyze



#### Statoscope



Built elaborated report of your bundle. Separates scripts from initial loading and asynchronous loading.



[Github Link](https://github.com/statoscope/statoscope)



#### Bundle Analyzer



[Github Link](https://github.com/webpack-contrib/webpack-bundle-analyzer)



#### Why?



Identifies why a package has been installed. Especially useful for transitive dependencies.



```sh

yarn why

pnpm why

```



### Webpack Alias: Remove 3-rd Party Code from Bundle



```js

const mockEmptyModule = path.resolve('./mock-empty-module.js');

// ...

config.resolve.alias['reactstrap/lib/Carousel.js'] = mockEmptyModule;

```



### Lazy Code Loading: On Viewport, on Interaction



The key principle is to avoid including code in the initial load that can be downloaded later. Instead, download it when a user is about to view it in their viewport, during idle time, or at the start of an interaction. 



For React, combine dynamic module import with Suspense.



[real world example](https://dev.to/dsitdikov/my-journey-to-accelerate-load-times-in-heavy-frontend-30c7/)



### Deduplication



If it's safe, align the minor versions of installed modules that are duplicated.



```sh

yarn dedupe

npm dedupe

pnpm dedupe

```



### Webpack: Magic Comments on Imports



Allows you to rename chunks, regroup, prefetch lazy chunks and more.



[link](https://webpack.js.org/api/module-methods/#magic-comments)



---



## React Tools



### Why Did You Render



A tool for detecting unnecessary re-renders. It can be used to find components that are re-rendered too often. Write 

messages to the console.



[link](https://github.com/welldone-software/why-did-you-render)



### React DevTools Profiler



Shows the time spent rendering each component and how many times it was rendered. To observe why it was rendered, 

enable the "Record why each component rendered while profiling" flag in the settings.



[link](https://chrome.google.com/webstore/detail/react-developer-tools/fmkadmapgofadopljbjfkapdkoienihi)



---



## Learning Resources



### Browser Rendering Optimization Course



Provides a solid basis for understanding how a browser renders a document and what happens behind the scenes.



[link](https://www.udacity.com/course/browser-rendering-optimization--ud860)



### Web App Performance Course



Reveals many subtleties and working practices about optimization that are not usually written about. 



[link](https://frontendmasters.com/courses/web-app-performance/)



---



## Metrics



This is a list of the most common metrics which may appear in articles, DevTools, Lighthouse, and other

various tools for working with web performance. Everything is sorted in the alphabetical order.



The factual data is primarily sourced from MDN, web.dev and w3c, however the short description has been rewritten and enhanced.



### CLS



**Cumulative Layout Shift**



Measurement Unit: Score (lower is better)



Shows how often users experience unexpected changes in the layout. It measures the 

instability of elements and their overall impact. For example, the banner element changes its height 

during the loading process, which causes a shift in the elements below.



[more details](https://web.dev/articles/cls)



### DCL



**DOMContentLoaded**



Measurement Unit: Milliseconds (ms)



Refers to the moment in a webpage's loading process when the DOM is completely parsed. And all deferred scripts have 

downloaded and executed. It doesn't wait for resources.



[more details](https://developer.mozilla.org/en-US/docs/Web/API/Document/DOMContentLoaded_event)



### FCP



**First Contentful Paint**



Measurement Unit: Milliseconds (ms)



Measures the time it takes for first bit of any actual content on a page to become visible on the screen. 

This includes text, images, background images, SVG elements, and non-white canvas elements.



[more details](https://web.dev/articles/fcp)



### FID



**First Input Delay**



Measurement Unit: Milliseconds (ms)



Measures the time it takes for the browser to respond to a user's first interaction. This interaction can 

include clicks, hovers, touches, and other user events.



[more details](https://web.dev/articles/fid)



### FP



**First Paint**



Measurement Unit: Milliseconds (ms)



Marks the first time the browser renders anything visually different from the default background color of the body.



### INP



**Interaction to Next Paint**



Measurement Unit: Milliseconds (ms)



Measures the time it takes for the browser to paint the next frame after a user interaction. 



[more details](https://web.dev/articles/inp)



### L



**On Load**



Measurement Unit: Milliseconds (ms)



Measures the time when the entire page and its resources are fully loaded. 

It includes all dependent resources: stylesheets, scripts, iframes, and images.



[more details](https://developer.mozilla.org/en-US/docs/Web/API/Window/load_event)



### LCP



**Largest Contentful Paint**



Measurement Unit: Milliseconds (ms)



Measures the time when the largest content block is rendered in the user viewport. The content may include images, 

background images, SVG, video, and text.



[more details](https://web.dev/articles/lcp)



### SI



**Speed Index**



Measurement Unit: Score (lower is better)



Measures how swiftly the contents of a page are visually populated. Technically, in a graph, it is represented 

by the area above the curve, which will approach 0 as the page loads faster.



[more details](https://developer.mozilla.org/en-US/docs/Glossary/Speed_index)



### TBT



**Total Blocking Time**



Measurement Unit: Milliseconds (ms)



Measures the time between [FCP](#FCP) and [TTI](#TTI) when the main thread was blocked for long enough to prevent input responsiveness. 

More specifically, it's the sum of the blocking time for each long task (>50 ms). For web frameworks, this time is 

usually consumed by virtual DOM renders and hydration.



[more details](https://web.dev/articles/tbt)



### TTI



**Time to Interactive**



Measurement Unit: Milliseconds (ms)



Measures the time when than at least for 5 seconds where weren't long tasks (>50ms) and

no more than two in-flight network GET requests.



[more details](https://web.dev/articles/tti)



### TTFB



**Time To First Byte**



Measurement Unit: Milliseconds (ms)



Measures when the first byte of data from the web server reaches the browser.



[more details](https://web.dev/articles/ttfb)