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

¿?

JavaScript Loading Priorities and Adaptive Loading

By Joan León

JavaScript Loading Priorities and Adaptive Loading

First, we will talk about adaptive loading, an essential technique in today's online world. Adaptive loading allows your website to adapt to different devices and internet capabilities, ensuring that users don't have to deal with extremely long loading times or performance issues. We will discuss techniques such as image optimization, progressive loading, and methods for evaluating site loading speed on different devices. Next, we will move on to resource loading prioritization, a technique that can truly make a difference in site performance. We will explore how the browser loads resources of a website and how HTML tags can be used to specify the loading priority of each resource. We will also share practical techniques such as loading custom fonts and deferred JavaScript to implement prioritized resource loading. By the end of the talk, you will have the knowledge to apply these techniques to your own projects and take user experience and site performance to the next level. So get ready to enhance your web development skills and create even more impressive websites!

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