[Javascirpt] What’s new in JavaScript (Google I/O ’19)

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:

巴特西

[Javascirpt] What’s new in JavaScript (Google I/O ’19)

Private variable in class:

class field syntax:

flatMap:

Object.fromEntries:

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