export let a=xx;
export const a=xx;
export {
	xxx,xxx,xxx
}
let a=12,b=5,c=99
export {a,b,c}

import * as mod1 from './mod1';
console.log(mod1) 
输出对象{a:12,b:5,c:99}

export function xx(){}

export class xxx{}

export default xx;

import * as mod from "./xxx"

import {a,b,c} from "./xxx"

import xxx from './mod';
console.log(xxx)
(只能引入export default xxx)
	

//模块的代码引入进来，不引入内部成员
import "./1.css"

//异步引入
import("./mod1"); 
是个promise   .then(x=>{}, err=>{})