Free JavaScript reference · Python timeline

JavaScript syntax and features timeline

Follow JavaScript from ES2015 to the latest published edition.

Explore twelve ECMAScript editions in order. Each free lesson explains useful syntax and built-in APIs, with examples, expected output, and common mistakes. ES2015 is also called ES6. This is a curated guide; the linked specifications define the complete editions.

Know variables, conditions, loops, and functions before starting. New to JavaScript? Start with Foundations. Browser APIs such as the DOM and fetch are separate from ECMAScript, and TypeScript has its own additional syntax.

1. Edition 6 · June 2015

   ES2015 (ES6): The modern JavaScript foundation

   Block-scoped variables, arrow functions, templates, destructuring, collections, promises, classes, and modules reshape everyday JavaScript.

   • Block scope with let and const
   • Arrow functions capture this
   • Template literals and interpolation
   • Destructuring, defaults, rest, and array spread
   • Map keys and Set membership
   • Promises compose eventual results
   • Class syntax over prototypes
   • Modules declare exports explicitly

   Editorial review October 26, 2026 · Published specification

2. Edition 7 · June 2016

   ES2016: Small additions with useful edge cases

   Exponentiation makes powers explicit, and includes supplies a membership test that can find NaN.

   • Exponentiation with **
   • Array includes and NaN

   Editorial review October 26, 2026 · Published specification

3. Edition 8 · June 2017

   ES2017: Async functions and convenient data views

   Async/await improves promise-based control flow, objects gain entry/value views, and text padding becomes a built-in operation.

   • Async/await keeps promise control flow readable
   • Object.entries() and Object.values()
   • Padding text with padStart and padEnd

   Editorial review October 26, 2026 · Published specification

4. Edition 9 · June 2018

   ES2018: Object copies and asynchronous cleanup

   Object rest/spread collects or copies properties, promise finally handles cleanup, and asynchronous iteration becomes language syntax.

   • Object rest and spread
   • Promise.finally() preserves settlement
   • Async generators and for await...of

   Editorial review October 26, 2026 · Published specification

5. Edition 10 · June 2019

   ES2019: Shape collections without extra bookkeeping

   Array flattening, object construction from entries, and optional catch bindings simplify common transformations.

   • flat() and flatMap() flatten one level
   • Object.fromEntries() builds a record
   • Catch without an unused binding

   Editorial review October 26, 2026 · Published specification

6. Edition 11 · June 2020

   ES2020: Safer optional access and larger integers

   Optional chaining, nullish defaults, BigInt, and allSettled make absence and asynchronous outcomes more explicit.

   • Optional chaining with ?.
   • Nullish defaults with ??
   • BigInt represents large integers
   • Promise.allSettled() keeps every outcome

   Editorial review October 26, 2026 · Published specification

7. Edition 12 · June 2021

   ES2021: Defaults, literal replacements, and first success

   Logical assignment avoids repeated access, replaceAll handles every occurrence, and Promise.any resolves on the first fulfillment.

   • Logical assignment operators
   • replaceAll() with a literal search
   • Promise.any() selects the first fulfillment

   Editorial review October 26, 2026 · Published specification

8. Edition 13 · June 2022

   ES2022: Class privacy, relative indexing, and module await

   Private fields and public class fields arrive with at(), Object.hasOwn(), and top-level await in modules.

   • Public fields and #private fields
   • Relative indexing with at()
   • Object.hasOwn() tests presence safely
   • Top-level await in modules

   Editorial review October 26, 2026 · Published specification

9. Edition 14 · June 2023

   ES2023: Array changes without mutating the original

   Copying array methods and findLast help preserve input data and search from the end.

   • toSorted(), toReversed(), toSpliced(), and with()
   • findLast() and findLastIndex()

   Editorial review October 26, 2026 · Published specification

10. Edition 15 · June 2024

    ES2024: Group records and expose promise controls

    Object.groupBy and Map.groupBy aggregate data, while Promise.withResolvers packages a promise with its settlement functions.

    • Object.groupBy() and Map.groupBy()
    • Promise.withResolvers() exposes settlement functions

    Editorial review October 26, 2026 · Published specification

11. Edition 16 · June 2025

    ES2025: Lazy iterator pipelines and new collection helpers

    Iterator helpers, Set operations, RegExp.escape, and Promise.try add useful building blocks without changing browser support overnight.

    • Iterator helpers form lazy pipelines
    • Set union, intersection, and difference
    • RegExp.escape() inserts literal search text
    • Promise.try() captures immediate throws

    Editorial review October 26, 2026 · Published specification

12. Edition 17 · June 2026

    ES2026: More expressive collections, bytes, and numeric checks

    Async collection, Map upserts, byte codecs, precise summation, JSON source access, error checks, and iterator sequencing join the standard.

    • Array.fromAsync() collects asynchronous values
    • Map getOrInsert and getOrInsertComputed
    • Uint8Array Base64 and hex codecs
    • Math.sumPrecise() reduces summation loss
    • JSON revivers can access primitive source text
    • Error.isError() checks error identity
    • Iterator.concat() sequences iterable sources

    Editorial review October 26, 2026 · Published specification