es 6,es 7,es 8文法まとめ===>(不定期更新)

let,const       ，       

const             

                this

       var self = this          

       ，this        ,     this     this

includes:
    const string = 'food';

    const substring = 'foo';

    console.log(string.includes(substring));
           。

string.repeat(str,count)

   string.length < count    str count == string.length  

  const name = 'Tiger';
    const age = 13;
    console.log(`My cat is named ${name} and is ${age} years old.`);

    let [a, b, c, d] = [1, 2, 3, 4];

    console.log(a);

    console.log(b);

    var luke = { occupation: 'jedi', father: 'anakin' };

    var occupation = luke.occupation;

    var father = luke.father;

    -------------------------------------------------------------

    let luke = { occupation: 'jedi', father: 'anakin' };

    let {occupation, father} = luke;

    console.log(occupation);

    console.log(father);

    ：

    function sumThree(a, b, c) {

        return a + b + c;

        }

    export { sumThree };

  ：

    import { sumThree } from 'math/addition';

es6       ：

function addTwoNumbers(x=0, y=0) {

    return x + y;

}

        ：

    function logArguments(...args) {

        for (let arg of args) {

            console.log(arg);

        }

    }

      ：

    Math.max(...[-1, 100, 9001, -32]);

    let cities = ['San Francisco', 'Los Angeles'];

    let places = ['Miami', ...cities, 'Chicago']; // ['Miami', 'San Francisco', 'Los Angeles', 'Chicago']

   :

    class Person {

        constructor(name, age, gender) {

            this.name  = name;

            this.age    = age;

            this.gender = gender;

        }

        incrementAge() {

        this.age += 1;

        }

    }

        

    let map = new Map();

    map.set('name', 'david');

    map.get('name');

    map.has('name');

      ，         

    func1(value1)

    .then(func2)

    .then(func3)

    .then(func4)

    .then(func5, value5 => {

    });

              

function* genFunc() {

    // (A)

    console.log('First');

    yield; //(B)

    console.log('Second'); //(C)

}

  :

    let array = ['1','2','3']

    if(array.includes('2')){

        console.log(' ')

    }

2**3 == 8 

  :

    let obj = {a: 1, b: 2, c: 3};

    Object.entries(obj).forEach(([key, value]) =>{

        console.log(key + ": " + value); //   a: 1, b: 2, c: 3

    })

            

  :

    async fetchData(query) =>{

        try {

            const response = await axios.get(`/q?query=${query}`);

            const data = response.data;

            return data;

        }

        catch (error) {

            console.log(error)

        }

    }

    fetchData(query).then(data => {

        this.props.processfetchedData(data)

    })