模块

export 和 import

一个模块导出(export)的变量才可以在另外一个变量中导入(import)

导出可以使用 export 和 export default

//写法1
const apiKey = "abc123"
export apiKey

//写法2
export const apiKey = "abc123"

//导出多个
const apiKey = "abc123"
const apiKey2 = ""
export {apiKey, apiKey2} //导出多个用大括号 括起来

//导出变量重命名
const apiKey = "abc123"
const apiKey2 = ""
export {apiKey as key, apiKey2} //导出重命名 就需要

导入写法

//导入 export变量 必须用大括号括起来 并且名称与导出名称一致
import {apiKey, apiKey2} from "./config"

//导入时重命名
import {apiKey as key, apiKey2} from "./config" //将导入的变量重命名使用

export default
设置模块的默认导出

//
export default const apiKey = "abc123"
//
const apiKey = "abc123"
export default apiKey

对于export default导出的变量导入时:

export default const apiKey = "abc123"

//导入时 名字可以随意指定 而且不需要大括号
import key from "./config" 

//当export和export default导出的变量一起导入
import key, {apiKey, apiKey2} from "./config" 

export不止可以导出变量还可以导出函数 class等

export function sum(a, b) {
    return a+b
}

export default class {
    
}