An unofficial, reader-focused rendering of the ECMAScript® Language Specification. It mirrors the source from tc39/ecma262 and restyles it for readability — it is not normative.

Live at https://kt3k.github.io/ecma262/ (the root redirects to the editor's draft). Every edition from the latest draft down to ES5.1 is served at /ecma262/<id>/.

A single Lume (Deno) project renders every edition. The per-edition input is ecma262/<id>/spec.html:

• draft … ES2015 are ecmarkup source; lume/scripts/build-chapters.mjs re-implements the subset of ecmarkup's build the site needs (numbering, xref resolution, grammar tokenisation, autolinking) with no ecmarkup dependency.
• ES5.1 predates ecmarkup, so its already-rendered official HTML goes through lume/scripts/build-chapters-es51.mjs, a re-skin ingester (see docs/es5.1-plan.md).

The whole site — the Lume project and its build scripts — lives under lume/ with a single lume/deno.json. lume/scripts/build-pages.ts adapts the generated chapters into Lume pages for one edition (driven by EDITION + BASE_PATH); lume/scripts/assemble-dist.mjs loops over every edition and folds the results into dist/ for GitHub Pages.

# one edition, locally (from lume/)
EDITION=es2024 BASE_PATH= deno task pages && deno task build

# the full combined site
deno task build      # → dist/

.
├── ecma262/                     # per-edition spec sources (the build inputs)
│   ├── draft/                   #   git submodule → tc39/ecma262
│   ├── es2026 … es2015/         #   vendored ecmarkup snapshots (spec.html + img/)
│   └── es5.1/                   #   vendored official HTML (re-skinned, not ecmarkup)
│
├── lume/                        # the whole site: Lume (Deno) project + build scripts
│   ├── deno.json                #   the one project config (imports, JSX, tasks)
│   ├── editions.json            #   single source of truth: id + title, newest-first
│   ├── _config.ts               #   plugins, static copy, on-this-page TOC
│   ├── _includes/               #   site chrome (page/header/sidebar/footer/…)
│   ├── scripts/                 #   build scripts (run via deno)
│   │   ├── build-pages.ts       #     EDITION/BASE_PATH → per-edition pages
│   │   ├── build-chapters.mjs   #     ecmarkup spec.html → per-chapter <Sec> JSX
│   │   ├── build-chapters-*.mjs #     ES5.1/ES3/ES1–ES2 re-skin ingesters
│   │   └── assemble-dist.mjs    #     build every edition → dist/
│   ├── styles.css, fonts/, …    #   the ecmarkup look + assets
│   └── (lib/, *.mdx, img/, _includes/chapters.json — gitignored, regenerated)
│
├── nextra-poc/                  # vendored Nextra comparison build (served at /nextra-poc/)
├── docs/                        # design & reference docs
│
├── .github/workflows/deploy.yml # CI: setup-deno → deno task build → GitHub Pages
├── deno.json                    # thin root: the build task (→ lume) + fmt config
└── AGENTS.md (CLAUDE.md →)       # project instructions

Generated per-edition content under lume/ (lib/, *.mdx, img/, _includes/chapters.json) is gitignored and regenerated per build, so nothing edition-specific is committed.

1. Vendor the spec: git clone --depth 1 --branch <tag> https://github.com/tc39/ecma262, then copy spec.html + img/ into ecma262/<id>/.
2. Append { "id": "<id>", "title": "…" } to lume/editions.json (newest-first).

That's it — the Lume build and assemble-dist pick it up automatically. (ES5.1 is the one exception: it is rendered HTML, not ecmarkup source, and routes through the re-skin ingester.)

• docs/es5.1-plan.md — ES5.1 re-skin architecture
• docs/tc39-deviations.md — where the styling intentionally differs from tc39.es (and why)
• docs/lume_migration_history.md — how the site moved from Nextra to Lume
• docs/emu-xref-investigation.md / docs/dl-header-investigation.md — build-chapters.mjs internals
• docs/typography-proposal.md — typography notes
• lume/README.md — Lume site internals

This is not the official specification. For the authoritative text see https://tc39.es/ecma262/.