对象解构语法在赋值语句的左侧使用了对象字面量
let node = { type: true, name: false } //既声明又赋值 let { type, name } = node; //或者先声明再赋值 let type, name ({type,name} = node); console.log(type);//true console.log(name);//false
type与name标识符既声明了本地变量，也读取了对象的相应属性值。
解构赋值表达式的值为表达式右侧的值。当解构表达式的右侧的计算结果为null或者undefined时，会抛出错误。
默认值
当你使用解构赋值语句时，如果所指定的本地变量在对象中没有找到同名属性，那么该变量会被赋值为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
你可以选择性地定义一个默认值，以便在指定属性不存在时使用该值。
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
赋值给不同的本地变量名
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这种语法表示要读取名为type的属性，并把它的值存储在变量localType上。该语法与传统对象字面量的语法相反
嵌套的对象结构
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}
当冒号右侧存在花括号时，表示目标被嵌套在对象的更深一层中（loc: {start: localS,end: localE}）
二 数据解构
数组解构的语法看起来跟对象解构非常相似，只是将对象字面量换成了数组字面量。
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
你也可以在解构模式中忽略一些项，并只给感兴趣的项提供变量名。
let colors = ["red","green","blue"]; let [,,thirdC] = colors; console.log(thirdC);//blue
thirdC之前的逗号是为数组前面的项提供的占位符。使用这种方法，你就可以轻易从数组任意位置取出值，而无需给其他项提供名称。
解构赋值
let colors = ["red","green","blue"], firstColor = "black", secondColor = "purple"; [firstColor,secondColor] = colors; console.log(firstColor);//red console.log(secondColor);//green
数组解构有一个非常独特的用例，能轻易的互换两个变量的值。
let a =1,b =2; [a,b] = [b,a]; console.log(a);//2 console.log(b);//1
嵌套的解构
let colors = ["red", ["green", "blue"], "yellow"]; let [firstC, [, ssc]] = colors; console.log(ssc);//blue
剩余项
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
使用剩余项可以进行数组克隆
let colors = ["red", "green", "blue"]; let [...restC] = colors; console.log(restC);//["red", "green","blue"]
三 混合解构
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