Interop 2024 closes with broad browser alignment
Interop 2024 wrapped up as the most successful year for the cross-browser compatibility project to date. All experimental browsers ended the year reporting a score of 99, with stable versions close behind. That level of interoperability helped push a number of web platform features into the "Baseline Newly available" category, meaning they are now supported across the latest versions of all major browsers.
Features that reached Baseline in 2024
Several features that were part of the Interop 2024 focus areas completed their journey to Baseline Newly available status during the year.
Registered custom properties
The @property rule and the CSS.registerProperty() static method, which allow you to define types and initial values for CSS custom properties, became Baseline Newly available in July 2024.
font-size-adjust
The font-size-adjust property scales fonts relative to a specified metric, such as x-height, so that fallback fonts appear to maintain the same visual size as the primary font. It also reached Baseline Newly available in July 2024.
requestVideoFrameCallback()
For video elements, the requestVideoFrameCallback() method schedules a callback to run when the next video frame is presented, functioning similarly to requestAnimationFrame() for video content. This API was added to Baseline Newly available in October 2024.
Scrollbar styling
The scrollbar-width property lets you control scrollbar thickness, while scrollbar-gutter reserves space for a scrollbar, preventing layout shifts when it appears or is hidden. Both properties became Baseline Newly available in December 2024.
transition-behavior
The transition-behavior: allow-discrete declaration enables transitions on properties that have discrete animation behavior. These properties cannot be interpolated; they flip from their start to end value at the halfway point. This property reached Baseline Newly available in August 2024.
text-wrap: balance
The text-wrap property, a shorthand for text-wrap-style and text-wrap-mode, controls how lines break in overflowing text. Its balance value is designed for short pieces of text like headlines. This property entered Baseline Newly available in March 2024.
Popover (close to the line)
Popover, which enables declarative overlays via HTML or the showPopover() method, nearly achieved Baseline Newly available status. A bug in the Safari implementation prevented it from crossing the threshold in 2024, but a fix is included in Safari Beta 18.3, so a proper announcement should follow soon.
Fixes for existing Baseline features
Some features in the Interop 2024 scope were already Baseline Newly available. For those, the work focused on resolving smaller discrepancies between browser implementations that could still cause real issues for developers.
CSS nesting
CSS nesting, which allows rules to be nested for shorter, more readable selectors, became Baseline Newly available in December 2023. Interop 2024 work targeted remaining interoperability problems with it.
Declarative Shadow DOM
The shadowrootmode attribute on <template> creates a shadow root without JavaScript, serving as a declarative counterpart to the attachShadow() method. It was part of the effort to smooth out remaining implementation differences.
Next up: Interop 2025
Proposals for the Interop 2025 focus areas are currently being finalized, with an announcement expected in February. To track features as they land in Baseline, the web.dev teams maintain a series on newly available Baseline features.
