Limits and roadmap

What it cannot do

• Generators and suspending await (the interpreter is a tree walker).
• Canvas, workers, event sources, WebSocket, WebRTC, service workers.
• Full Request / Response and the streams built on them.
• Complete Selectors coverage: :focus-visible, dir=auto and named-item access.
• UTF-16 offsets in CharacterData methods for non-BMP text.
• Speed comparable to a JIT browser.

Levers, biggest first

1. A bytecode VM for the script engine: it would add generators and suspending await, and is faster than walking the tree.
2. Binding shape. A large share of remaining failures are interface-conformance tests for objects that exist but lack members, or exist without an exposed interface (Navigator, History, Storage, Location).
3. Request and Response, currently the weakest part of URL-adjacent tests.
4. Cross-realm constructors, for example DOMParser reached through a frame.
5. Selectors long tail, as above.

What we will not do

We will not stub interfaces for features that do not exist just to raise a number. Feature detection on real pages would then lie.

Where the numbers come from

Every claim on this page is checked against the Web Platform Tests. Gaps are ranked by comparing our per-file pass counts with a reference browser's, not by guessing.