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

Incredible Demos

  • By
    MooTools, mediaboxAdvanced, and Mexico

    The lightbox is probably one of my favorite parts of the Web 2.0 revolution. No more having to open new windows (which can bog down your computer quite a bit) to see a larger image, video, etc. Instead, the item loads right into the...

  • By
    CSS Kwicks

    One of the effects that made me excited about client side and JavaScript was the Kwicks effect.  Take a list of items and react to them accordingly when hovered.  Simple, sweet.  The effect was originally created with JavaScript but come five years later, our...

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!