Deconstruction assignment

1.1. Array deconstruction assignment

    // Assign to a variable through an array
    let arr = [1.2.3]
    console.log(arr[0]);
    console.log(arr[1]);
    console.log(arr[2]);
    let [a,b,c] = [1.2.3]
    console.log(a);
    console.log(b);
    console.log(c);
    
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1.1.1. Pattern matching

If the pattern is the same on both sides of the equal sign, the variable on the left will be assigned the corresponding value

  let [a,[[b],c]] = [1The [[2].3]]
    console.log(a);
    console.log(b);
    console.log(c);
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1.1.2. Incomplete deconstruction

// Not completely deconstructed
    let [x,y,u] = [1.2.3.4]
    console.log(x);
    console.log(y);
    console.log(u);
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1.1.3. Nested pattern

  let [a,[[b],c]] = [1The [[2].3]]
    console.log(a);
    console.log(b);
    console.log(c);
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1.1.4. The default value

 // Specify a default value
    let [f = true] = []
    console.log(f);
    let [a,b="y"] = ['a']
    console.log(b);
    // Note that es6 internal use === check whether undefined if undefined the default value takes effect
    let [x = 1] = [null]
    let [y = 2] = [undefined]
    console.log(x); // null 
    console.log(y); / / 2
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1.1.4.1. Lazy evaluation

// lazy evaluation
    function f(){
        return 'fff'
    }
    // let [x = f()] = [1]
    let [x = f()] = []
    console.log(x);
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1.1.4.2. Default values can refer to other variables that are destructively assigned

// Default values can refer to other variables that are destructively assigned as long as the variables are already declared
    // let [x= 1,y=x] = []
    // console.log(x); / / 1
    // console.log(y);
    // let [x = y,y=1] = [] // from left to right
    // let [y = 1 , x = y] = []
    // console.log(x);
    // console.log(y);
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2. Object deconstruction assignment

2.1. Define usage notes

 let person = {
        name:"chris".age:33
    }
    // let {name,age} = person;
    // Note that object deconstruction is not the same as array and has nothing to do with order
    let {age:age,name:name} = person;
    console.log(name);
    console.log(age);
    
    let {sex} = person;
    console.log(sex); // Unsuccessfully destruct returns undefined
    // What is really assigned is the nature of the latter object's deconstruction assignment
    // The attribute of the same name is first found and assigned to the variable of the latter
    let {name:name1} = person
    console.log(name1);
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2.2. Inherited properties can be fetched

    const obj1 = {};
    const obj2 = {name:'laney'}
    Object.setPrototypeOf(obj1,obj2)
    // obj1.__proto__ = obj2
    const {name} = obj1;
    console.log(name);
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2.3. Specify default values

// The value of the object attribute is strictly === undefined
const {x = 1} = {x:undefined}
const {y = 3} = {y:null}
console.log(x);
console.log(y);
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