Use React DOM Resource Hints

Impact: HIGH (reduces load time for critical resources)

React DOM provides APIs to hint the browser about resources it will need. These are especially useful in server components to start loading resources before the client even receives the HTML.

prefetchDNS(href): Resolve DNS for a domain you expect to connect to
preconnect(href): Establish connection (DNS + TCP + TLS) to a server
preload(href, options): Fetch a resource (stylesheet, font, script, image) you'll use soon
preloadModule(href): Fetch an ES module you'll use soon
preinit(href, options): Fetch and evaluate a stylesheet or script
preinitModule(href): Fetch and evaluate an ES module

Example (preconnect to third-party APIs):

tsx

import { preconnect, prefetchDNS } from 'react-dom'

export default function App() {
  prefetchDNS('https://analytics.example.com')
  preconnect('https://api.example.com')

  return <main></main>
}

Example (preload critical fonts and styles):

tsx

import { preload, preinit } from 'react-dom'

export default function RootLayout({ children }) {
  // Preload font file
  preload('/fonts/inter.woff2', { as: 'font', type: 'font/woff2', crossOrigin: 'anonymous' })

  // Fetch and apply critical stylesheet immediately
  preinit('/styles/critical.css', { as: 'style' })

  return (
    <html>
      <body>{children}</body>
    </html>
  )
}

Example (preload modules for code-split routes):

tsx

import { preloadModule, preinitModule } from 'react-dom'

function Navigation() {
  const preloadDashboard = () => {
    preloadModule('/dashboard.js', { as: 'script' })
  }

  return (
    <nav>
      <a href="/dashboard" onMouseEnter={preloadDashboard}>
        Dashboard
      </a>
    </nav>
  )
}

When to use each:

API	Use case
`prefetchDNS`	Third-party domains you'll connect to later
`preconnect`	APIs or CDNs you'll fetch from immediately
`preload`	Critical resources needed for current page
`preloadModule`	JS modules for likely next navigation
`preinit`	Stylesheets/scripts that must execute early
`preinitModule`	ES modules that must execute early

Reference: React DOM Resource Preloading APIs