1.import,export——模块化

exp.js

export let a = 10;

export let person = {name:'lily'}

export function test(){console.log("hello");}

export class Animal{

}

index.js

import {a} form './exp.js';

a = 100;//报错 a是常量不能改

console.log(a) //10


===========

import {a,person} form './exp.js';

// a = 100;//报错 a是常量不能改

//如果是基本类型，不能改，如果是对象如{a,person}就可以修改
person.name = 'mickey';//对象可以修改属性
console.log(a) //10
console.log(person.name) //mickey

===========

import {a,person,Animal} form './exp.js';

let ani = new Animal();
console.log(ani)

导入方式比较

index.js

import {exp} from './exp.js'
console.log(exp.a);
console.log(exp.Animal);

=============

一次性导入某个文件的所有模块并重新命名
import * as exp from './exp.js';

console.log(exp.a);
console.log(exp.Animal);

将所有要导入的元素放入default里面

// exp.js

let a = 10;
let person = {name:'tom'};
function test(){console.log('hello')};
class Animal{}

export default{
    a,person,test,Animal
}

//default只能使用一次

// index.js

import Exp from './exp.js';
console.log(Exp.a);
console.log(Exp.Animal);