Chrome 96 Unveiled: WebAssembly Reference Types, HTTPS DNS, Priority Hints Explained

TL;TR

Chrome 96 was released on 2021‑11‑16.

It adds 20 features, including 12 new ones and 4 origin‑trial experiments.

Key highlights: WebAssembly Reference Types, HTTPS DNS records, Priority Hints, and WebAssembly Dynamic Tiering.

WebAssembly Reference Types

Chrome 96 ships the WebAssembly Reference Types proposal, allowing values of type externref to be passed between JavaScript and WebAssembly without manual integer encoding.

Previously, only 32‑ and 64‑bit integers and floats were supported, forcing developers to encode strings or objects as byte arrays, which generated bulky glue code and reduced performance.

Reference Types enable direct handling of complex data such as strings and objects, reducing the need for glue code and opening the door for future proposals like GC, Interface Types, and type imports.

The proposal is authored by Andreas Rossberg, a former Google engineer and current WebAssembly spec editor.

HTTPS DNS Records

Chrome 96 fully supports the HTTPS DNS record type, allowing browsers to discover a site’s HTTPS, HTTP/2, and HTTP/3 capabilities directly from DNS, eliminating an extra round‑trip. example.com 3600 IN HTTPS 1 . alpn="h3,h2" When present, Chrome always initiates an HTTPS connection on the first request, improving security and performance.

The feature is based on the IETF draft "Service binding and parameter specification via the DNS (DNS SVCB and HTTPS RRs)" and has been default‑enabled since Chrome 91.

Priority Hints

Chrome 96 introduces the importance attribute (values: high, low, auto) to let developers influence resource loading priority.

<!-- Set image priority --><br/><img src="/images/test.png" importance="high" /><br/><br/><!-- Set fetch priority --><br/><script>fetch("https://example.com/", { importance: "low" }).then(r => {});</script>

Using importance="high for critical assets, such as background images, can noticeably reduce Largest Contentful Paint, as demonstrated by Google Flight.

Priority Hints are a WICG proposal currently supported only in Chrome.

WebAssembly Dynamic Tiering

Chrome 96 trials Dynamic Tiering for WebAssembly, altering V8’s compilation strategy to avoid eager full‑program optimization.

V8 contains two compilers: Liftoff (baseline, one‑pass) and TurboFan (optimizing, multi‑pass). Previously, Liftoff compiled quickly and TurboFan re‑compiled all functions in the background, wasting CPU and memory for rarely used code.

Dynamic Tiering defers TurboFan compilation to functions that are executed repeatedly, mirroring JavaScript tiered compilation and reducing resource consumption.

Benchmarks show Liftoff is 5‑10× faster than TurboFan, while TurboFan‑optimized code can be up to 100% faster; the new strategy balances startup speed and execution performance.

Conclusion

The four Chrome 96 features—WebAssembly Reference Types, HTTPS DNS records, Priority Hints, and Dynamic Tiering—revisit fundamental web concepts (DNS, HTTPS, HTTP, compilation) while showcasing how modern browsers evolve to improve security, performance, and developer experience.