javascript解构赋值

此文章为意译并非直译，可参考具体原文

解构赋值具体干什么？

解构赋值是javascript中的一个表达式语法糖，帮助开发者将数组，对象属性解构出来并且直接赋值到具体变量上面。

直接来段代码感受下

let a,b,rest;
[a,b] = [10,20];
console.log(a);// 10,
console.log(b);// 20;
[a,b,...rest] = [10,20,30,40,50,60];
console.log(a); // 10
console.log(b); // 20
console.log(rest);// [30,40,50,60]

简单实践，将a,b的值进行交互

let a=10,b=20;
[a,b]=[b,a];
console.log(a);// 20
console.log(b);// 10;

解构赋值具体使用方式

数组对象进行解构赋值

// 1. 从已有对数组中解构赋值
let foo = ['one','two','three'];
let [a,b] = foo;
console.log(a);
console.log(b);

// 2. 从字面量中解构赋值
let [a,b] = [1,2];

// 3. 在解构赋值对时候设置默认值
let [a=5, b=10] = [1];
console.log(a); // 输出：1
console.log(b); // 输出：10

// 4. 解构从函数返回对数组
function getArr(){
    return [1,2]
}
let [a,b] = getArr();

// 5. 解构对时候，忽略特殊位置对值
let [a,,b] = [1,2,3];
// 全部忽略
[,,] = [1,2,3];

// 6. 解构对时候将数组的其他值赋值给变量
let [a,...b] = [1,2,3,4,5];
console.log(a);// 1
console.log(b);// [2,3,4,5]

对象数据进行解构赋值

// 1. 解构对象
let obj = {name:'hello',age:18};
let {name,age} = obj;
console.log(name);// hello;
console.log(age);// 18
// 2. 解构字面量对象
let name,age;
({name,age} = {name:'hello',age:18});// 结果和上面一样,注意，这里为什么需要用`()`包裹起来呢?
// 独立的写法
let {name,age} = {name:'hello',age:18};

// 3. 解构的时候，设置别名
let obj = {name:'hello',age:18};
let {name:nameA,age:ageA} = obj;
console.log(nameA);// hello
console.log(ageA);// 18
// 4. 设置默认值，这个和数组解构类似
let obj = {name:'hello',age:18};
let {name='tom',age=20,city='sh'}=obj;
console.log(city);// sh
// 5. 设置默认值，同时又设置别名
let obj = {n:'hello',age:18};
let {n:name='tom',age:a=19,city:c='sh'} = obj;
console.log(name); // hello
console.log(a);    // 18
console.log(c);    // sh
// 6. 设置函数参数的默认值
function drawES2015Chart({size = 'big', cords = {x: 0, y: 0}, radius = 25} = {}) {
  console.log(size, cords, radius);
  // do some chart drawing
}
drawES2015Chart({
  cords: {x: 18, y: 30},
  radius: 30
});

嵌套对象解构和数组解构

let data = {
  title:'objetAdnArray',
  list:[
    {
      id:1,
      des:'第一个对象',
      proList:[]
    },
    {
      id:2,
      des:'第二个对象',
      proList: []
    }
  ]
}

let {
  title,
  list:[{id,des}]
} = data;

console.log(title); // objetAdnArray
console.log(id);    // 1
console.log(des);   // 第一个对象

for of 循环中使用解构

var people = [
  {
    name: 'Mike Smith',
    family: {
      mother: 'Jane Smith',
      father: 'Harry Smith',
      sister: 'Samantha Smith'
    },
    age: 35
  },
  {
    name: 'Tom Jones',
    family: {
      mother: 'Norah Jones',
      father: 'Richard Jones',
      brother: 'Howard Jones'
    },
    age: 25
  }
];
for (let {name: n, family: {father: f}} of people) {
  console.log('Name: ' + n + ', Father: ' + f);
}

// "Name: Mike Smith, Father: Harry Smith"
// "Name: Tom Jones, Father: Richard Jones"

解析对象的字段传递给

function userId({id}) {
  return id;
}

function whois({displayName, fullName: {firstName: name}}) {
  console.log(displayName + ' is ' + name);
}

var user = { 
  id: 42, 
  displayName: 'jdoe',
  fullName: { 
      firstName: 'John',
      lastName: 'Doe'
  }
};

console.log('userId: ' + userId(user)); // "userId: 42"
whois(user); // "jdoe is John"

将变量最为解构的key

let key = 'z';
let {[key]:foo} = {z:'this is z'};
console.log(foo); // this is z
// 注意，这个用户很类似对象字面量赋值的用法
let obj = {
    [key]:'hello'
}

obj.z // hello

总结：es6提供了许多语法糖，在客户端使用的时候需要通过进行编译才能运行，而在服务器端nodejs已经很好的支持了