2018-04-12 11:13:57 +08:00
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## CMD的基本语法
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### CMD的概念
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2018-12-09 17:23:30 +08:00
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**CMD**（Common Module Definition）：同步模块定义。CMD专门用于浏览器端，模块的加载是同步的。模块在使用时才会加载执行。
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2018-04-12 11:13:57 +08:00
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2018-04-13 09:43:52 +08:00
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[**CMD规范**]()：是 **[SeaJS](http://seajs.org/)** 在推广过程中对模块化定义的规范化产出。
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### SeaJS
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2018-04-12 11:13:57 +08:00
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SeaJS：一个基于CMD规范实现的模块化开发解决方案。
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2018-04-13 09:43:52 +08:00
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官网链接：
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- <http://seajs.org/>
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- <https://github.com/seajs/seajs>
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推荐学习链接：
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- <http://www.zhangxinxu.com/sp/seajs/>
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- <http://es6.ruanyifeng.com/#docs/module>
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2018-04-12 11:13:57 +08:00
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### 暴露模块的方式
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2018-04-13 09:43:52 +08:00
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> 不管是定义没有依赖的模块，还是定义有依赖的模块，参数只有一个，那就是 function。
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**定义没有依赖的模块**：
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```javascript
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define(function (require, exports, module) {
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exports.xxx = value
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//暴露模块
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module.exports = value
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})
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```
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参数只有一个，那就是 function。function 里有三个参数：
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**定义有依赖的模块**：
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```javascript
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//定义有依赖的模块
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define(function (require, exports, module) {
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//引入依赖的模块(同步的方式)
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var module2 = require('./module2')
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//引入依赖的模块(异步的方式)
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require.async('./module3', function (m3) {
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})
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//暴露模块
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exports.xxx = value
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})
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```
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上面的代码可以看到，在引入依赖的模块时，有两种引入的方式：同步和异步。
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### 引入模块的方式
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```javascript
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define(function (require) {
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var m1 = require('./module1')
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var m4 = require('./module4')
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m1.show()
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m4.show()
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})
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```
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## SeaJS的使用举例（自定义模块）
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### 1、创建项目结构
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在工程文件中新建如下目录：
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```
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js
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| libs
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| sea.js
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| modules
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| module1.js
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| module2.js
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| module3.js
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| module4.js
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| main.js //主模块
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index.html
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```
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### 2、下载SeaJS，并导入
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- 官网: <https://seajs.github.io/seajs/docs/#downloads>
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- GitHub：<https://github.com/seajs/seajs>
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在官网下载`sea.js`文件，然后将其拷贝到项目的`js/libs/`目录中。这样的话，就导入成功了。
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### 3、自定义模块
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（1）module1.js：
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```javascript
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//定义没有依赖的模块
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define(function (require, exports, module) {
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let name = '我是 module1 中的内容';
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function foo1() {
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return name;
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}
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//暴露模块
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module.exports = { foo1 }; //暴露出去的是 foo1这个函数对象
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});
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```
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（2）module2.js：
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```javascript
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//定义没有依赖的模块
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define(function (require, exports, module) {
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let name = '我是 module2 中的内容';
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function foo2() {
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console.log(name);
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}
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//暴露模块
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module.exports = foo2; //可以理解成：exports就是 foo2 这个函数
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});
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```
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（3）module3.js:
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```javascript
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//定义没有依赖的模块
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define(function (require,exports,module) {
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let data = '我是 module3 中的内容';
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function foo3() {
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console.log(data);
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}
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//暴露模块
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exports.module3 = { foo3 }; //可以理解成：给 export 对象暴露了 module3 这个属性，这个属性里有foo3 这个函数。
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});
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```
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（4）module4.js：
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这个模块依赖了 module2 和 module3。
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```javascript
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//定义有依赖的模块
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define(function (require, exports, module) {
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let name = '我是 module4 中的内容';
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//同步的方式引入 module2
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let myModule2 = require('./module2');
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myModule2();
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//异步的方式引入 module3
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require.async('./module3', function (myModule3) {
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myModule3.module3.foo3();
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});
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function foo4() {
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console.log(name);
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}
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exports.foo4 = foo4;
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})
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```
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（5）main.js：
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- `module1.js`没有依赖其他的模块，它是独立的
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- `module4.js`依赖了`module2`和`module3`。
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因此，让`main.js`依赖`module1.js`和`module4`就够了。
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main.js：
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```javascript
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//主模块（主模块不需要导出）
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define(function (require) {
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//导入 module1
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let module1 = require('./module1');
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console.log(module1.foo1()); //执行foo1函数后，将返回值打印
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//导入 module4
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let module4 = require('./module4');
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module4.foo4();
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});
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```
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（6）index.html：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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</head>
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<body>
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<!-- 引入 sea.js库 -->
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<script src="js/libs/sea.js"></script>
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<script>
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// 引入主模块
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seajs.use('./js/modules/main.js');
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</script>
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</body>
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</html>
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```
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打印结果：
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2018-10-02 22:10:26 +08:00
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2020-04-13 19:00:31 +08:00
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## others
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### SeaJS 的介绍
|
|
|
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|
|
SeaJS：一个基于CMD规范实现的模块化开发解决方案。
|
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|
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|
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|
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|
|
|
|
作者：Alibaba 玉伯。
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官网：<http://seajs.org/>
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GitHub：<https://github.com/seajs/seajs>
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|
现在官网变成了：<https://seajs.github.io/seajs/docs/>
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特性：
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- 简单友好的模块定义规范。
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- 自然直观的代码组织方式。
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|
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|
|
|
### RequireJS（AMD）、SeaJS（CDM）、CommonJS、ES6 的对比
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1、RequireJS 和 AMD：
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异步模块定义，特点是依赖前置。
|
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|
2、SeaJS 和 CMD：
|
|
|
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|
|
|
|
|
|
|
|
|
|
|
|
|
同步模块定义。
|
|
|
|
|
|
|
|
|
|
|
|
```javascript
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|
|
|
|
|
// 所有模块都通过 define 来定义
|
|
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|
|
|
define(funtion(require, exports, module) {
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|
|
|
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|
|
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|
|
//通过 require 引入依赖
|
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|
|
var $ require(`jquery`);
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var Spinning = require(`./spinning`);
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})
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```
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|
3、CommonJS：
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|
|
以上三个都是 ES5里面的规范。
|
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|
|
4、ES6：
|
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|
|
ES6的特性：export/import
|
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