ES6 数据解构教程：对象与数组赋值、默认值及剩余项用法

对象解构基础

一对象解构

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。

默认值处理

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

变量重命名

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

嵌套对象解构

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}）

数组解构应用

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。

变量交换技巧

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

嵌套数组与剩余项

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"]

混合解构总结

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

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ES6 数据解构：对象与数组的高级用法详解