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

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

Reference

prefetchDNS(href)

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

import{prefetchDNS}from'react-dom';

functionAppRoot(){
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.

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';

functionAppRoot(){
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';

functionCallToAction(){
constonClick = ()=>{
prefetchDNS('http://example.com');
startWizard();
}
return(
<buttononClick={onClick}>Start Wizard</button>
);
}
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