Private variable in class:

class Counter {  #count = 0; // cannot be access publicly  get value () {    return this.#count;  }  incremenet(){    this.#count++;  }}

 

class field syntax:

Previously you need to call 'super'

class Animal {  constructor (name) {    this.name = name  }}class Cat extends Animal {  constructor (name) {    super(name);    this.likesBaths = false;  }  meow () {    // ...  }}

But now, we don't need to, you can use classs field:

class Animal {  constructor (name) {    this.name = name  }}class Cat extends Animal {  likesBaths = false;  meow () {    // ...  }}

 

Above two features are supported in latest Chrome and Node.js.

 

flatMap:

const duplicate = x => [x, x];console.log([2,3,4].flatMap(duplicate)); // [2, 2, 3, 3, 4, 4]

 

Object.fromEntries:

Reverse opreation of Object.entries, it transform [['x', 42], ['y', 50]] too {x: 42, y: 50}:

const object = {x: 42, y: 50, abc: 9001}const result = Object.fromEntries(  Object.entries(object)    .filter(([key, value]) => key.length === 1) // only take x, y, ingore abc    .map(([key, value]) => [key, value * 2])) // {x: 84, y: 100}

It is also support to transform back and from Javascirpt Map.

 

globalThis:

using 'globalThis' to handle all the envs.

 

Intl: