queryLocalFonts

By  on  

One of the larger downloads when requesting a webpage are custom fonts. There are many great techniques for lazy loading fonts to improve performance for those on poor connections. By getting insight into what fonts the user has available, we can avoid loading custom fonts. That's where queryLocalFonts comes in -- an native JavaScript function to gather user font information.

queryLocalFonts is an async function that requires user permission via a browser prompt when first executed. queryLocalFonts returns an array of FontData objects which contain information about all available fonts:

const localFonts = await window.queryLocalFonts();

// [FontData, FontData, ...]

/*
{
  family: "Academy Engraved LET",
  fullName: "Academy Engraved LET Plain:1.0",
  postscriptName: "AcademyEngravedLetPlain",
  style: "Plain",
}
*/

If you'd like to target a specific font face, you can also directly query the postscriptName property:

const canelaFonts = await window.queryLocalFonts({
  postscriptNames: ["Canela", "Canela-Bold"],
});

// [FontData, FontData, ...]

With queryLocalFonts you can leverage a fonts a user already has instead of downloading expensive custom fonts. The prompt for permissions seems like it would deter users from allowing the API, however. It's so cool that this API exists though!

Recent Features

  • By
    CSS Animations Between Media Queries

    CSS animations are right up there with sliced bread. CSS animations are efficient because they can be hardware accelerated, they require no JavaScript overhead, and they are composed of very little CSS code. Quite often we add CSS transforms to elements via CSS during...

  • By
    CSS Filters

    CSS filter support recently landed within WebKit nightlies. CSS filters provide a method for modifying the rendering of a basic DOM element, image, or video. CSS filters allow for blurring, warping, and modifying the color intensity of elements. Let's have...

Incredible Demos

Discussion

  1. Thank u for explaning of the use of queryLocalFonts to optimize web performance by leveraging user’s local fonts. However, do you think the permission prompt might be a significant barrier for widespread adoption of this technique?

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!