Remove [LegacyNoInterfaceObject] from FontFaceSet IDL

at a glance

what changed and why

The Web IDL extended attribute [LegacyNoInterfaceObject] tells the browser not to expose an interface as a named property on the global object. Applied to FontFaceSet, it meant that self.FontFaceSet (and window.FontFaceSet) was undefined in Chrome, and the constructor property was absent from FontFaceSet.prototype.

This deviated from the CSS Font Loading specification, which does not include [LegacyNoInterfaceObject], and from Firefox and Safari where window.FontFaceSet is accessible. Chrome 151 removes the annotation, making the behaviour consistent.

Note on instantiation: because the IDL defines no constructor(), calling new FontFaceSet() continues to throw TypeError: Illegal constructor — this is correct spec-mandated behaviour. FontFaceSet instances are obtained via document.fonts, not by direct construction.

what changes

example

// Chrome 151+: FontFaceSet is accessible as a global
console.log(typeof FontFaceSet); // "function"

// Check if document.fonts is a FontFaceSet (now works cross-browser)
console.log(document.fonts instanceof FontFaceSet); // true

// Useful for type-checking / polyfill detection
if (typeof FontFaceSet !== 'undefined') {
  // FontFaceSet interface available
  document.fonts.ready.then(() => {
    console.log('All fonts loaded');
  });
}

// Still works (unchanged) — always use document.fonts, not new FontFaceSet()
const fonts = document.fonts;
fonts.add(new FontFace('MyFont', 'url(myfont.woff2)'));

browser support

see also

• Chrome Platform Status — Remove [LegacyNoInterfaceObject] from FontFaceSet IDL
• CSS Font Loading — FontFaceSet interface