const config = {
 host: 'localhost',
 port: 80
}

let { host } = config

// config.js
export default {
 host: 'localhost',
 port: 80
}

// app.js
import config from './config'

let { host } = config
console.log(host) // => localhost
console.log(config.host) // => localhost

// app.js
import { host } from './config'

console.log(host) // => undefined

import { host } from './config'

// config.js
export default {
 host: 'localhost',
 port: 80
}

// app.js
import { host } from './config'
console.log(host) // => undefined

const a = { b: 1 }
const { b } = a 

const b = a.b 

import { resolve } from 'path' 

export default {

 b: 1

} 

import { b } from './a' 

import { b } from './a' 

a.default.b 

export const b = 1 

export default {
 host: 'localhost',
 port: 80
}

module.exports.default = {
 host: 'localhost',
 port: 80
}

import { host as hostName } from './config' // 解构赋值中不能用 as

let obj = {
 a: {
 b: 'hello',
 }
}

let {a: {b}} = obj // import 语句中不能这样子写
console.log(b) // => helllo

// a.js
import { foo, bar } from "./b"
// b.js
export default {
 foo: "foo",
 bar: "bar"
}

import b from './b'
let { foo, bar } = b

// a.js
import { foo, bar } from "./b"
// b.js
let foo = "foo"
let bar = "bar"
export { foo, bar }

// a.js
import { foo, bar } from "./b"
// b.js
export let foo = "foo"
export let bar = "bar"