ES6 模块化笔记

// ES6模块
import { stat, exists, readFile } from 'fs';

 1 // 写法1
 2 export var firstName = 'Michael';
 3 export var lastName = 'Jackson';
 4 export var year = 1958;
 5 
 6 // 写法2
 7 var firstName = 'Michael';
 8 var lastName = 'Jackson';
 9 var year = 1958;
10 
11 export {firstName, lastName, year};
12 
13 // 写法3
14 
15 var firstName = 'Michael';
16 var lastName = 'Jackson';
17 var year = 1958;
18 
19 export {
20   firstName as variable1,
21   lastName as variable2,
22   year as variable3
23 };
24 
25 // 方法1
26 export function multiply(x, y) {
27   return x * y;
28 };
29 
30 // 方法2
31 function v1() { ... }
32 function v2() { ... }
33 
34 export { v1,v2 };
35 
36 // 方法3
37 function v1() { ... }
38 function v2() { ... }
39 export {
40   v1 as streamV1,
41   v2 as streamV2,
42   v2 as streamLatestVersion
43 };

1 import { lastName as surname } from './profile';
2 foo();
3 // import命令是编译阶段执行的，在代码运行之前，所以foo已经被赋值
4 import { foo } from 'my_module';

import 'lodash';

 1 // circle.js
 2 
 3 export function area(radius) {
 4   return Math.PI * radius * radius;
 5 }
 6 
 7 export function circumference(radius) {
 8   return 2 * Math.PI * radius;
 9 }
10 
11 // main.js
12 
13 import { area, circumference } from './circle';
14 
15 console.log('圆面积：' + area(4));
16 console.log('圆周长：' + circumference(14));
17 
18 // 第二种写法
19 import * as circle from './circle';
20 
21 console.log('圆面积：' + circle.area(4));
22 console.log('圆周长：' + circle.circumference(14));

1 // export-default.js
2 export default function () {
3   console.log('foo');
4 }
5 
6 // import-default.js
7 import customName from './export-default';
8 customName(); // 'foo'

 1 // modules.js
 2 function add(x, y) {
 3   return x * y;
 4 }
 5 export {add as default};
 6 // 等同于
 7 // export default add;
 8 
 9 // app.js
10 import { default as xxx } from 'modules';
11 // 等同于
12 // import xxx from 'modules';

1 // 正确
2 export var a = 1;
3 
4 // 正确
5 var a = 1;
6 export default a;
7 
8 // 错误
9 export default var a = 1;