一 對象解構

對象解構語法在賦值語句的左側使用了對象字面量

let node = {
    type: true,
    name: false
}

//既聲明又賦值
let {
    type,
    name
} = node;

//或者先聲明再賦值
let type, name
({type,name} = node);
console.log(type);//true
console.log(name);//false

type與name標識符既聲明瞭本地變數，也讀取了對象的相應屬性值。

解構賦值表達式的值為表達式右側的值。當解構表達式的右側的計算結果為null或者undefined時，會拋出錯誤。

預設值

當你使用解構賦值語句時，如果所指定的本地變數在對象中沒有找到同名屬性，那麼該變數會被賦值為undefined

let node = {
    type: true,
    name: false
},
    type, name, value;
({type,value,name} = node);

console.log(type);//true
console.log(name);//false
console.log(value);//undefined

你可以選擇性地定義一個預設值，以便在指定屬性不存在時使用該值。

let node = {
        type: true,
        name: false
    },
    type, name, value;
({
    type,
    value = true,
    name
} = node);

console.log(type);//true
console.log(name);//false
console.log(value);//true

賦值給不同的本地變數名

let node = {
    type: true,
    name: false,
    value: "dd"
}
let {
    type: localType,
    name: localName,
    value: localValue = "cc"
} = node;
console.log(localType);
console.log(localName);
console.log(localValue);

type:localType這種語法表示要讀取名為type的屬性，並把它的值存儲在變數localType上。該語法與傳統對象字面量的語法相反

嵌套的對象結構

let node = {
type: "Identifier",
name: "foo",
loc: {
    start: {
        line: 1,
        column: 1
    },
    end: {
        line: 1,
        column: 4
    }
}
}

let {
loc: localL,
loc: {
    start: localS,
    end: localE
}
} = node;

console.log(localL);// start: {line: 1,column: 1},end: {line: 1,column: 4}
console.log(localS);//{line: 1,column: 1}
console.log(localE);//{line: 1,column: 4}

當冒號右側存在花括弧時，表示目標被嵌套在對象的更深一層中（loc: {start: localS,end: localE}）

二 數據解構

數組解構的語法看起來跟對象解構非常相似，只是將對象字面量換成了數組字面量。

let colors = ["red", "blue", "green"];
let [firstC, secondC, thirdC, thursC = "yellow"] = colors;
console.log(firstC//red
console.log(secondC);//blue
console.log(thirdC);//green
console.log(thursC);//yellow

你也可以在解構模式中忽略一些項，並只給感興趣的項提供變數名。

let colors = ["red","green","blue"];

let [,,thirdC] = colors;
console.log(thirdC);//blue

thirdC之前的逗號是為數組前面的項提供的占位符。使用這種方法，你就可以輕易從數組任意位置取出值，而無需給其他項提供名稱。

解構賦值

let colors = ["red","green","blue"],
    firstColor = "black",
    secondColor = "purple";
[firstColor,secondColor] = colors;
console.log(firstColor);//red
console.log(secondColor);//green

數組解構有一個非常獨特的用例，能輕易的互換兩個變數的值。

let a =1,b =2;
[a,b] = [b,a];
console.log(a);//2
console.log(b);//1

嵌套的解構

 let colors = ["red", ["green", "blue"], "yellow"];
let [firstC, [, ssc]] = colors;
console.log(ssc);//blue

剩餘項

let colors = ["red", "green", "blue"];
let [firstC, ...restC] = colors;
console.log(firstC);
console.log(...restC);
console.log(restC[0]);//green
console.log(restC[1]);//blue

使用剩餘項可以進行數組克隆

let colors = ["red", "green", "blue"];
let [...restC] = colors;
console.log(restC);//["red", "green","blue"]

三 混合解構

let node = {
type: "Identifier",
name: 'foo',
loc: {
    start: {
        line: 1,
        column: 1
    },
    end: {
        line: 1,
        column: 4
    }
},
range: [0, 3]
}

let {
type,
name: localName,
loc: {
    start: {
        line: ll
    },
    end: {
        column: col
    }
},
range: [, second]
} = node;

console.log(type);//Identifier
console.log(localName);//foo
console.log(ll);//1
console.log(col);//4
console.log(second);//3