explaingit

tc39/ecma262

Analysis updated 2026-06-24

★ 15,625HTMLAudience · developerComplexity · 4/5Setup · moderate

TLDR

Source of the ECMA-262 spec that formally defines JavaScript. Build it locally with npm and read the rendered version at tc39.es/ecma262.

Mindmap

mindmap
  root((ecma262))
    Inputs
      Spec source files
      TC39 proposals
      Community PRs
    Outputs
      Rendered HTML spec
      Standards document
    Use Cases
      Look up JavaScript semantics
      Track new language features
      Propose changes via TC39
    Tech Stack
      HTML
      Node
      Ecmarkup
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Code map

Detail Auto

An interactive map of this repo's files and how they connect — its source is parsed live in your browser. Click Visualize to build it.

filefunction / class

What do people build with it?

USE CASE 1

Read the canonical JavaScript spec to settle a behavior question

USE CASE 2

Build the spec locally to preview a proposed edit

USE CASE 3

Submit a fix or clarification PR to ECMA-262

USE CASE 4

Follow how a TC39 proposal lands in the language

What is it built with?

HTMLNodeEcmarkup

How does it compare?

tc39/ecma262alshedivat/al-foliofederico-busato/modern-cpp-programming
Stars15,62515,59015,574
LanguageHTMLHTMLHTML
Setup difficultymoderateeasyeasy
Complexity4/52/51/5
Audiencedeveloperresearcherdeveloper

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · moderate Time to first run · 30min

Building the spec requires Node and an npm install before npm run build.

In plain English

This repository contains the source for ECMA-262, the official specification document that defines the ECMAScript language, which is the standard that JavaScript is built on. In other words, this is where the rules of JavaScript are written down in a formal, standards-body format. The source is processed to produce a human-readable version of the spec, available at tc39.es/ecma262. New language features for JavaScript don't appear in the spec directly, they start as proposals. Those proposals follow the TC39 process, a multi-stage review system (Stage 0 through finished) tracked in a separate proposals repository. Anyone can contribute a new proposal by following the process outlined in the contributing guide. The repository also supports local development: cloning it and running npm install followed by npm run build produces the spec in the out directory. Community discussion happens on the ES discourse forum and a Matrix chat channel.

Copy-paste prompts

Prompt 1
Show me how to clone tc39/ecma262 and build the rendered HTML spec locally
Prompt 2
Explain how the TC39 stage process moves a JavaScript proposal from Stage 0 to shipped
Prompt 3
Find the section of ECMA-262 that defines how == coercion works and quote it back to me
Prompt 4
Write a guide for submitting an editorial fix PR to ecma262 that respects the contributing rules

Frequently asked questions

What is ecma262?

Source of the ECMA-262 spec that formally defines JavaScript. Build it locally with npm and read the rendered version at tc39.es/ecma262.

What language is ecma262 written in?

Mainly HTML. The stack also includes HTML, Node, Ecmarkup.

How hard is ecma262 to set up?

Setup difficulty is rated moderate, with roughly 30min to a first successful run.

Who is ecma262 for?

Mainly developer.

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