Key new features

ES2015 (ES6)

• let and const
• Class syntax
• Method syntax in classes and object literals
• Arrow functions
• Template literals
• Destructuring
• Property value shorthands (object literal entries with same key/value)
• Rest and spread for arrays and arguments
• ES6 modules: export and import

ES2016

Not much

ES2017

• async/await
• Trailing commas in function parameter lists and calls
• Object.entries()

ES2018

• Object rest/spread
• Promise.prototype.finally()

ES2019

• Object.fromEntries()

ES2020

• Optional chaining: ?.
• Nullish coalescing operator: ??

ES2021

• Logical assignment operators: ||= &&= ??=

ES2022

• Top-level await
• (some of) private class fields and methods (instance and static)
• Array.prototype.at including negative indices

ES2023

• Array.findLast() and .findLastIndex()
• Immutable array methods
  • .toReversed()
  • .toSorted()
  • .toSpliced()
  • .with() (updates one entry)

Pre-Stage-4

• https://github.com/tc39/proposals
• https://github.com/babel/proposals