The features of Interop 2025 are now known. The list, whose items are to be made implemented and stable across browsers by the end of the year, includes anchor positioning, the View Transitions API, the Storage Access API, and more for a total of 19 focus areas.
With popovers already at over 90% browser support, CSS anchor positioning allows positioning an element in relation to another element. Positioning tooltips, popovers, and dropdowns thus becomes easier and declarative, eliminating the need for JavaScript and third-party libraries. Anchor positioning is currently not supported in Firefox or Safari.
The View Transition API provides a mechanism for easily creating animated transitions between different website views. The API has two major use cases: same-document view transitions (e.g., in a SPA), and transitioning between documents in a multi-page application (MPA). Same-document view transitions should be stable in every browser by the end of 2025.
Transitions have numerous benefits for users. Well-animated transitions between pages are likely to reduce the perception of latency and help users stay in context. Transitions are also a common feature of mobile applications. Web developers can use view transitions to reduce the user experience gap between native mobile applications and web applications.
As with CSS anchor positioning, support across all major browsers would eliminate the need for custom JavaScript or third-party libraries. Performance and smoothness are key requirements for animations. View transitions previously required significant effort and the use of large amounts of CSS and JavaScript, which introduced jank in animations, thus defeating the original purpose.
The Storage Access API helps manage cookies across different origins while respecting privacy and security standards. The API provides methods that allow embedded resources that have a legitimate need for third-party cookies or unpartitioned state access to check whether they currently have access and, if not, to request access from the user agent.
The MDN website explains:
Depending on the browser, the user will be asked whether to grant access to the requesting embed in slightly different ways.
- Safari shows prompts for all embedded content that has not previously received storage access.
- Firefox only prompts users after an origin has requested storage access on more than a threshold number of sites.
- Chrome shows prompts for all embedded content that has not previously received storage access. It will however automatically grant access and skip prompts if the embedded content and embedding site are part of the same related website set.
In addition to the three features detailed previously, Interop totals 19 active focus areas for 2025 and 5 active investigations (e.g., Accessibility testing, Gamepad API testing, Mobile testing, Privacy testing, and WebVTT). Developers can review progress on the listed items at any time through the online Interop 2025 Dashboard.
Developers on Reddit emphasized the importance of the new features.
[sharlos]:
Excited for the Navigation API finally getting support. Will finally eliminate the need for complex libraries for SPA navigation.[nickbreaton]:
Anchor positioning is going to be huge!
Browser makers Apple, Google, Microsoft, and Mozilla, alongside consultancies Bocoup and Igalia are sponsoring Interop, a project to promote web browser interoperability. Interop 2024 ended with a median of 98% of tests passing across browsers in the stable release channel and 99% in the canary/nightly release channel.