Amber implements the WinterTC (Ecma TC55, formerly WinterCG) baseline so Web-platform code written for edge runtimes can run unchanged where the APIs overlap. This baseline is part of the Stable scope in CURRENT_SCOPE.md.

ECMA-429 minimum common Web API

API	Behavior
`DOMException`	Global constructor with `name`, `message`, `code`, and legacy constants
`globalThis.self`	Alias of `globalThis`
`reportError(error)`	Calls `onerror` when set
`PromiseRejectionEvent`	Dispatched on unhandled rejections through `onunhandledrejection`
`navigator.userAgent`	`Amber/<version>`
`navigator.hardwareConcurrency`, `language`, `platform`	Present
`URLPattern`	`test()` and `exec()` with `:param` groups
`ByteLengthQueuingStrategy`, `CountQueuingStrategy`	Global constructors
`ReadableStream.from`	Iterable and async-iterable sources

Runtime keys

package.json "exports" conditions include wintercg and wintertc ahead of node. import.meta.resolve uses the same resolver, so a package that publishes "wintercg": "./winter.js" resolves to that file instead of its "node" entry.

import.meta.main is true for the CLI entry module. import.meta.env maps process environment variables.

Sockets API

const { connect } = require("amber:sockets");

const socket = connect(
  { hostname: "example.com", port: 443 },
  { secureTransport: "on" },
);
// socket.readable and socket.writable are Web streams.

secureTransport: "on" and socket.startTls() run a real rustls client handshake. Connecting with TLS to a plain TCP port fails with a TLS error instead of silently staying in cleartext.

Tests

bash

cargo test --test wintertc_compliance_tests -- --test-threads=1

WinterTC baseline

ECMA-429 minimum common Web API

Runtime keys

Sockets API

Tests