Interop 2024: half-year progress report
Interop 2024 set out to close browser compatibility gaps across a prioritized list of web platform features. Six months in, the results show measurable progress. Chrome's experimental implementation score has climbed from 83 to 90, and the stable browser score sits at 85 following the Chrome 126 release in June. The overall experimental interop score has gained 10 points. Several once-inconsistent features have now reached interoperability across the major engines.
Popover API
The Popover API reached Baseline (Newly available) in April 2024. It standardizes a long list of UI patterns that previously required hand-rolled JavaScript: menus, tooltips, teaching overlays, and selection dialogs. Developers no longer need custom logic to enforce one-open-at-a-time behavior, implement light-dismiss on outside clicks, or wrestle with z-index to keep layers on top.
Because the browser handles these details natively, the result is both less code and better accessibility. Tokopedia, for instance, cut a significant amount of React code by using Popover with a polyfill for older engines. Browser support for the API spans Chrome 114, Edge 114, Firefox 125, and Safari 17.
Advanced custom properties with @property
The CSS @property rule goes beyond the simple name/value model of standard custom properties. It lets you register a property's allowed syntax — for instance, a color, number, or length — and declare whether it inherits. You can also set an initial value, which is used when the property is not otherwise defined.
This feature contributes to Firefox's experimental score today and will add to the stable score when Firefox 128 ships in July. It joins Baseline as Newly available with support in Chrome 85, Edge 85, Firefox 128, and Safari 16.4.
font-size-adjust
With the font-size-adjust property, you can tune the height of lowercase letters relative to uppercase ones. That matters when a font falls back: adjusting this ratio keeps the fallback legible at small sizes, where metric mismatches become most noticeable.
Included in the experimental score for Chrome, font-size-adjust will also nudge the stable score when Chrome 127 ships. Supported in Chrome 127, Edge 127, Firefox 3, and Safari 16.4, the property is now Baseline Newly available.
text-wrap: balance
The text-wrap: balance value asks the browser to compute balanced line wrapping for a block of text. It is particularly useful for headings, preventing one-or-two-word orphans on the final line. Safari recently added support, and work continues on failing tests in other engines to make the feature uniform everywhere. Current support includes Chrome 114, Edge 114, Firefox 121, and Safari 17.5.
Beyond the headline features
These major APIs are just part of the story. Every test that now passes across engines is an interoperability issue that won't surface in production. With the midpoint behind it, the question is how much of the remaining gap can be closed before the end of the year.
