prefetchDNS

prefetchDNS lets you eagerly look up the IP of a server that you expect to load resources from.

prefetchDNS("https://example.com");

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Reference

prefetchDNS(href)

To look up a host, call the prefetchDNS function from react-dom.

import { prefetchDNS } from 'react-dom';

function AppRoot() {
  prefetchDNS("https://example.com");
  // ...
}

See more examples below.

The prefetchDNS function provides the browser with a hint that it should look up the IP address of a given server. If the browser chooses to do so, this can speed up the loading of resources from that server.

Parameters

• href: a string. The URL of the server you want to connect to.

Returns

prefetchDNS returns nothing.

Caveats

• Multiple calls to prefetchDNS with the same server have the same effect as a single call.
• In the browser, you can call prefetchDNS in any situation: while rendering a component, in an Effect, in an event handler, and so on.
• In server-side rendering or when rendering Server Components, prefetchDNS only has an effect if you call it while rendering a component or in an async context originating from rendering a component. Any other calls will be ignored.
• If you know the specific resources you’ll need, you can call other functions instead that will start loading the resources right away.
• There is no benefit to prefetching the same server the webpage itself is hosted from because it’s already been looked up by the time the hint would be given.
• Compared with preconnect, prefetchDNS may be better if you are speculatively connecting to a large number of domains, in which case the overhead of preconnections might outweigh the benefit.

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Usage

Prefetching DNS when rendering

Call prefetchDNS when rendering a component if you know that its children will load external resources from that host.

import { prefetchDNS } from 'react-dom';

function AppRoot() {
  prefetchDNS("https://example.com");
  return ...;
}

Prefetching DNS in an event handler

Call prefetchDNS in an event handler before transitioning to a page or state where external resources will be needed. This gets the process started earlier than if you call it during the rendering of the new page or state.

import { prefetchDNS } from 'react-dom';

function CallToAction() {
  const onClick = () => {
    prefetchDNS('http://example.com');
    startWizard();
  }
  return (
    <button onClick={onClick}>Start Wizard</button>
  );
}