Why this talk?

Web

Performance

Product

Web Almanac

JavaScript

Web Almanac

JavaScript

Web Almanac

JavaScript

Web Almanac

JavaScript

Web Almanac

JavaScript

Web Almanac

JavaScript

Adaptive Loading

 @media (min-width: 50em) {
   article {
     column-count: 2;
   }
 }

 window
  .matchMedia('(min-width: 768px)')
  .matches
import { useMediaQuery } from 'usehooks-ts'

export default function Component() {
  const matches = useMediaQuery('(min-width: 768px)')

  return (
    <div>
      {`The view port is 
		${matches ? 'at least' : 'less than'} 
    	768 pixels wide`}
    </div>
  )
}
import { useEffect, useState } from 'react'

function useMediaQuery(query: string): boolean {
  const getMatches = (query: string): boolean => {
    // Prevents SSR issues
    if (typeof window !== 'undefined') {
      return window.matchMedia(query).matches
    }
    return false
  }

  const [matches, setMatches] = useState<boolean>(getMatches(query))

  function handleChange() {
    setMatches(getMatches(query))
  }

  useEffect(() => {
    const matchMedia = window.matchMedia(query)

    // Triggered at the first client-side load and if query changes
    handleChange()

    // Listen matchMedia
    if (matchMedia.addListener) {
      matchMedia.addListener(handleChange)
    } else {
      matchMedia.addEventListener('change', handleChange)
    }

    return () => {
      if (matchMedia.removeListener) {
        matchMedia.removeListener(handleChange)
      } else {
        matchMedia.removeEventListener('change', handleChange)
      }
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [query])

  return matches
}

export default useMediaQuery

This property is used to leverage the user's Data Saver preferences.

This property is used to fine-tune data transfer to use less bandwidth.

This property is the CPU core count. It is used to limit costly JavaScript execution and reduce CPU intensive logic when a device can't handle it well.

This property is used to reduce memory consumption on low-end devices.

import { useNetworkStatus } from 'react-adaptive-hooks/network';
import { useSaveData } from 'react-adaptive-hooks/save-data';
import { useHardwareConcurrency } from 'react-adaptive-hooks/hardware-concurrency';
import { useMemoryStatus } from 'react-adaptive-hooks/memory';
import { useMediaCapabilitiesDecodingInfo } from 'react-adaptive-hooks/media-capabilities';
import React from 'react';

import { useNetworkStatus } from 'react-adaptive-hooks/network';

const MyComponent = () => {
  const { effectiveConnectionType } = useNetworkStatus();

  let media;
  switch(effectiveConnectionType) {
    case 'slow-2g':
      media = <img src='...' alt='low resolution' />;
      break;
    case '2g':
      media = <img src='...' alt='medium resolution' />;
      break;
    case '3g':
      media = <img src='...' alt='high resolution' />;
      break;
    case '4g':
      media = <video muted controls>...</video>;
      break;
    default:
      media = <video muted controls>...</video>;
      break;
  }
  
  return <div>{media}</div>;
};
import type { EffectiveConnectionType } from '@sbt-web/hooks';

interface Hooks {
  saveData?: boolean | null;
  effectiveConnectionType?: EffectiveConnectionType | null;
  deviceMemory?: number | null;
}

const shouldReduceDataUse = ({
  saveData = null,
  effectiveConnectionType = null,
  deviceMemory = null,
}: Hooks): boolean => {
  const saveDataSignal = saveData ?? false;
  const ectSignal = effectiveConnectionType ?? '4g';
  const deviceMemorySignal = deviceMemory ?? Infinity;

  return saveDataSignal || ectSignal !== '4g' || deviceMemorySignal <= 2;
};

export default shouldReduceDataUse;

JavaScript Loading Priorities

preload
prefetch
preconnect
dns-prefetch
prerender
modulepreload

<head>
  <link rel="preload" as="script" href="critical.js">
</head>
<link rel="preload" href="ComicSans.woff2" as="font" type="font/woff2" crossorigin>
Link: </css/style.css>; rel="preload"; as="style"
import(_/* webpackPreload: true */_ "CriticalChunk")

Preload critical assets

</>

</>

async or defer

<script async src="script.js">

<script defer src="script.js">

async

defer

Progressive Hydration

¿?