test_dev.js

import add from './add.js'; // 可以不用 add 名称
//import {sub} from './sub.js'; //sub 必须为 sub.js 导出的函数名
import * as sub from './sub.js'; // 把 sub.js 用一个类来导入
let name = "linson";
const age = 16;

function getInfo (name, age = 25) {let obj = {name: name, age: age};
    return obj;
}

let obj = getInfo (name);
let string = `name:${obj.name},age:${obj.age}`;
console.log (string);

let res = add (1, 2, 3);
console.log ("add res:" + res);

res = sub.sub (1, 2, 3);
console.log ("sub res:" + res);

add.js

function add (...args) {
    let res = 0;
    for (let arg of args) {res += arg;}
    return res;
};

export default add;

sub.js

function sub (...args) {
    let res = 0;
    for (let arg of args) {res -= arg;}
    return res;
};

export {sub};