A nano-sized `preconnect` hint wrapper.

rel, preconnect, dns-prefetch, web, performance, webperf
npm install preconnect@1.0.1



A nano-sized preconnect hint wrapper.

ES5 (.js) version

Uncompressed gzip Brotli

ES6 (.mjs) version

Uncompressed gzip Brotli

preconnect is a very small script that allows you to programmatically invoke a preconnect hint to any host to mask connection latency. The script is designed so that you can invoke this hint whenever is appropriate for your application.


Since preconnect is Just JavaScript™, you can install it with npm as a production dependency:

npm i preconnect --save

If you're not the npm type, grab one (or both) of the minified versions in this repo's dist folder. There are two minified versions:

  • preconnect.min.js is the Babel-fied ES5 build. It assigns a variable named preconnect on the window.
  • preconnect.min.mjs is the untransformed minified ES6 build. Its default export is a function eponymously named preconnect.


import preconnect from "preconnect";

const preconnecter = new preconnect({
  // Injects `dns-prefetch` hints in addition to `preconnect` hints
  getDns: true

// Preconnects to a link as the user hovers over it
document.getElementById("some-link").addEventListener("mouseover", event => {
}, {
  // Execute this event handler code only once avoid multiple injections of hints
  once: true

In the above example, an early connection is established to the host specified in an <a> element's href value. This could potentially speed up navigation to that host for the user, improving the perceived performance of the navigation.


When you instantiate a new instance of preconnect, you can pass in an options object. There are two options:

  • getDns (default: false)
    Inject a dns-prefetch hint in addition to a preconnect hint. Some browsers don't support preconnect, but some of those browsers do support dns-prefetch. Enabling this ensures those browsers still receive some kind of benefit.
  • timeout (default: 0)
    This script can use requestIdleCallback to take advantage of idle browser time. This helps to reduce monopolization of the main thread so that the page is more responsive to user input. This option specifies, in milliseconds, the deadline by which requestIdleCallback must inject the resource hint elements into the document <head>. A value of 0 (the default) disables the use of requestIdleCallback entirely.


If you'd like to contribute, please file an issue first so we can discuss. Because I'd like to keep this script very small and simple, new features aren't likely to be added unless the weight they add can be justified.

Author info

My name is Jeremy Wagner. I'm an independent web performance consultant. I write about web stuff, and sometimes I even get to talk about web stuff. I also ramble on Twitter @malchata and make web performance videos on YouTube.