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  • [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:

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  • 原文地址:https://www.cnblogs.com/Answer1215/p/10847120.html
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