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
    Convert XML to JSON with JavaScript

    If you follow me on Twitter, you know that I've been working on a super top secret mobile application using Appcelerator Titanium.  The experience has been great:  using JavaScript to create easy to write, easy to test, native mobile apps has been fun.  My...

  • By
    Page Visibility API

    One event that's always been lacking within the document is a signal for when the user is looking at a given tab, or another tab. When does the user switch off our site to look at something else? When do they come back?

Incredible Demos

  • By
    CSS Scoped Styles

    There are plenty of awesome new attributes we've gotten during the HTML5 revolution:  placeholder, download, hidden, and more.  Each of these attributes provides us a different level of control over an element on the page, but there's a new element attribute that allows...

  • By
    Hot Effect: MooTools Drag Opacity

    As you should already know, the best visual features of a website are usually held within the most subtle of details. One simple trick that usually makes a big different is the use of opacity and fading. Another awesome MooTools functionality is...

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!