ECMAScript Version

Version	Official Name	Date	Description
	JavaScript 1.0	1995	by Brendan Eich
ES1	ECMAScript 1	1997	ECMA-262
ES2	ECMAScript 2	1998
ES3	ECMAScript 3	1999
ES4	ECMAScript 4		未发布
ES5	ECMAScript 5	2009
ES6	ECMAScript 2015	2015
	ECMAScript 2016	2016
	ECMAScript 2017	2017
	ECMAScript 2018	2018
	ECMAScript 2019	2019
	ECMAScript 2020	2020
	ECMAScript 2021	2021
	ECMAScript 2022	2022
	ECMAScript 2023	2023
ES.Next			下一个版本

tip

• 今年采纳的建议，发布到下一年版本，因此会相差一年版本号

stage	for	note
stage 0	Strawperson
stage 1	Proposal
stage 2	Draft	描述准确
stage 3	Candidate	实现,等待用户使用反馈
stage 4	Finished	准备添加到 标准

👀

• Stage 3 - 接下来可能会加入到语言中的功能特性
  • Import Assertions
  • JSON Modules
  • Intl.DisplayNames
  • proposal-temporal
    • Temporal - 替代 Date
  • 2023
    • array group, groupToMap
      • https://github.com/tc39/proposal-array-grouping
    • Array - toReversed, toSorted, toSpliced, with
      • https://github.com/tc39/proposal-change-array-by-copy
    • Array.fromAsync
• modules-import-hooks-refactor
  • stage 1
  • import 过程可控
• Function.memo
• await generateItems().toArray()
  • tc39/proposal-iterator-helpers
• Array.fromAsynctc39/proposal-array-from-async

syntax	Chrome	Name
?.	Chrome80	Optional chaining
??	Chrome80	Nullish coalescing operator
??=	Chrome85	Nullish coalescing assignment

• es5 和 es6 是一个分界线
  • 2018 年所有浏览器支持 es6
  • 之后统一版本概念变弱 - 都以功能特性为单位
• tc39/proposals
• TC39 Process
  • https://tc39.es/process-document/
  • Finished Proposals
  • Active Proposals
  • Stage 1 Proposals
  • Stage 0 Proposals
  • Inactive/Withdrawn Proposals
• ECMAScript Language Specification
• 参考
  • Tarjan's strongly connected components algorithm
  • tc39/agendas
  • finished-proposals
  • https://caniuse.com/#search=es6
  • compat-table
    • 2016+
  • https://en.wikipedia.org/wiki/ECMAScript
  • https://www.proposals.es/

ECMAScript 2023

• findLast, findLastIndex
  • {Array, %TypedArray%}.prototype.findLastIndex
  • {Array, %TypedArray%}.prototype.findLast
• Hashbang Grammar - JS 直接只为可执行脚本

#!/usr/bin/env node

ECMAScript 2022

// Class Fields
class Counter extends HTMLElement {
  // 私有
  #val = 0;

  get #x() { return #val; }
  set #x(value) {
    this.#val = value;
  }

  #inc() {
    this.#val ++
  }

  // 静态
  static #blue = "#0000ff";
  static getBlue() {
    return this.#blue
  }
}

// regex 索引
// d -> indices
/a+(?<Z>z)?/d.exec('xaaaz').indices

// Top-level await
await Promise.resolve()

// static block
class C {
  static {
    // statements
  }
}

// error cause
try {
  throw new Error('error', { cause: err });
} catch (e) {
  console.log('Caused by', e.cause);
}

// Array#at
[,-1].at(-1)

ECMAScript 2021

• FinalizationRegistry
  • 注册 GC 回调

String.prototype.replaceAll;

Promise.any;

// WeakRef.prototype.deref
new WeakRef(() => 1);

// Logical Assignment Operators
a ||= b;
a &&= b;
a ??= b;

// Numeric separators
1_000_000_000;

ECMAScript 2020

• for-in 顺序

// String.prototype.matchAll
// 要求 RegEx 必须有 g 标识
'aa'.matchAll(/a/g);

// 动态 import
import('./foo.js');

// 模块元信息
import.meta;

BigInt;

// Promise.all 会在第一个异常时终止
Promise.allSettled;

globalThis;

// Optional Chaining
undefined?.b;

// Nullish coalescing Operator
undefined ?? null ?? 0 ?? 1;

ECMAScript 2019

• JSON superset
  • U+2028 LINE SEPARATOR, U+2029 PARAGRAPH SEPARATOR
• Function.prototype.toString revision
• Well-formed JSON.stringify
  • 避免返回错误 Unicode escape

// Optional catch binding
try {
} catch {}

Symbol.prototype.description;

Object.fromEntries([['k', 'v']]);

// String.prototype.{trimStart,trimEnd}
' 1 '.trimStart().trimEnd();

String.prototype.matchAll;

// Array.prototype.{flat,flatMap}
[[1], [2]].flat();
[0, 0].flatMap((_, i) => [1]);

ECMAScript 2018

• Lifting template literal restriction

// Regex Named Group
/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/u.exec('2015-01-02')
// Regex s -> dot all, single line
/foo.bar/s.test('foo\nbar');
// Regex Lookbehind Assertions
/(?<=\D)\d/
/(?<!\D)\d/
// Regex Unicode Property Escapes
// \p{UnicodePropertyName=UnicodePropertyValue}
// General_Category, Script, Script_Extensions
//
// \p{LoneUnicodePropertyNameOrValue}
// Alphabetic, Uppercase, Lowercase, White_Space, Noncharacter_Code_Point, Default_Ignorable_Code_Point, Any, ASCII, Assigned, ID_Start, ID_Continue, Join_Control, Emoji_Presentation, Emoji_Modifier, Emoji_Modifier_Base
//
// http://unicode.org/Public/UNIDATA/PropertyValueAliases.txt
// http://unicode.org/Public/UNIDATA/PropertyAliases.txt
// http://unicode.org/reports/tr18/#RL1.2
/^\p{Decimal_Number}+$/u.test('𝟏𝟐𝟑𝟜𝟝𝟞𝟩𝟪𝟫𝟬𝟭𝟮𝟯𝟺𝟻𝟼')

// Object Rest/Spread
const {a,...rest} = {a:1,b:2,...{c:3}}

// Promise#finally
Promise.prototype.finally;

// Asynchronous Iteration
// [Symbol.asyncIterator]
for await (const line of readLines()) {
  console.log(line);
}
async function* readLines(){
  yield await Promise.resolve('Line 1')
  yield 'Line 2'
}

ECMAScript 2017

• Shared Memory and Atomics

Object.values;
Object.entries;

'1'.padEnd(4, ' ');
'1'.padStart(4, ' ');

Object.getOwnPropertyDescriptors;

// 方法参数容许多余逗号
console.log(true);

// async,await
async function run() {
  await Promise.resolve();
}

ECMAScript 2016

Array.prototype.includes;

// Exponentiation
1 ** 2; // Math.pow(1,2)

ECMAScript 2015

// array function
() => 1;

// let, const
let a = 1;
const b = 1;

// for-of
for (const v of [1]);

// Map, Set
new Map();
new Set();

// Symbol
const mySym = new Symbol();

// class
class Car {
  constructor() {}
}

// promise
Promise.resolve();

// 默认参数, rest 参数
function hello(name = 'world', ...props) {}

const { a, b } = { a: 1, b: 2 };

String.prototype.includes;
String.prototype.startsWith;
String.prototype.endsWith;

Array.from('abc');
[(1, 2)].keys();
[(1, 2)].find((v) => v == 1);
[(1, 2)].findIndex((v) => v == 1);

Math.trunc;
Math.sign;
Math.cbrt;
Math.log2;
Math.log10;

Number.isInteger;
Number.isSafeInteger;

isFinite(1 / 0);
isNaN(false);

ECMAScript 5

'use strict';

'Hello'.charAt(0);
'Hello'[0];

// 多行 string
console.log(
  'Hello \
Wener!',
);

// 允许关键字作为属性名
const a = { new: 'yes' };

String.prototype.trim;

Array.isArray([]);
Array.prototype.forEach;
Array.prototype.map;
Array.prototype.filter;
Array.prototype.reduce;
Array.prototype.reduceRight;
Array.prototype.every;
Array.prototype.some;
Array.prototype.indexOf;
Array.prototype.lastIndexOf;

JSON.parse('{}');
JSON.stringify({});

Date.now();
Date.prototype.toISOString;
Date.prototype.toJSON;

// getter,setter
const a = {
  get name() {
    return '';
  },
  set name(v) {
    console.log(v);
  },
};

// mgmt
Object.create;
Object.defineProperty;
Object.defineProperties;
Object.getOwnPropertyDescriptor;
Object.getOwnPropertyNames;
Object.getPrototypeOf;
Object.keys;
// protect
Object.preventExtensions;
Object.isExtensible;
Object.seal;
Object.isSealed;
Object.freeze;
Object.isFrozen;

// 允许多余逗号
// {a:1,}
// [1,]