了解javascript中的modules、import和export

modules:必须写在<script  type="module" src="index.js"></script>

import：必须引用export的

import { sum, difference, product, quotient } from './functions.js'

别名

import {

  sum as add,

  difference as subtract

} from './functions.js'

模块名

import * as mathFunctions from './functions.js'

调用mathFunctions.sum

module还可以这样用

// 命名导入/导出 

export const name = 'value'

import { name } from '...'

// 默认导出/导入

export default 'value'

import anyName from '...'

// 重命名导入/导出 

export { name as newName }

import { newName } from '...'

// 命名 + 默认 | Import All

export const name = 'value'

export default 'value'

import * as anyName from '...'

// 导出列表 + 重命名

export {

  name1,

  name2 as newName2

}

import {

  name1 as newName1,

  newName2

} from '...'