CMD规范（通用模块定义规范）（翻译）

最近在使用sea.js。大家知道sea.js遵循CMD规范。该规范的英文说明很简洁，我试着翻译了一下，旨在交流。

Common Module Definition

通用模块定义规范

This specification addresses how modules should be written in order to be interoperable in browser-based environment. By implication, this specification defines the minimum features that a module system must provide in order to support interoperable modules.

本规范规定如何定义和书写执行在浏览器环境中的js模块，这就是说，本规范定义了一个模块的最小API，这些API提供与该模块系统的交互。

• Modules are singletons.

模块都是单例的。

• New free variables within the module scope should      not be introduced.

模块范围内的自由变量不应该被引入。

• Execution must be lazy.

模块的执行是按需执行的。

Module Definition

A module is defined with define keyword, which is a function.

模块是使用关键字“define”定义的一个函数。

define(factory);

1. The define function accepts a      single argument, the module

factory.define函数接受一个参数，模块工厂

1. The factory may be a function or      other valid values.

Factory可能是一个函数，或是一个可验证值

1. If factory is a function, the first      three parameters of the function, if specified, must be      "require", "exports", and "module", in that      order.

如果factory是一个函数，如果参数指定了，这个函数的前三个参数，按照顺序这三个参数是“require”，“exports”，“module”

1. If factory is not a function, then      the module's exports are set to that object.

如果factory不是一个函数，模块的exports必须设置成一个对象。

Module Context

In a module, there are three free variables: require, exports and module.

模块中三个变量：require，exports和module

define(function(require, exports, module) {

// The module code goes here

});

The require Function

1. require is      a function

require是一个函数

1. require accepts a module identifier.

require接受一个模块标识

1. require returns the exported API of the foreign module.

require返回一个外部模块对外公开的API

1. If requested module cannot be returned, require should return null.

如果请求的模块没有返回API，require必须返回null

1. require.async is a function require.async是一个函数
1. require.async accepts a list of module identifiers and a       optional callback function.

require.async接受一个模块标识列表和一个回调函数

1. The callback function receives module exports as       function arguments, listed in the same order as the order in the first       argument.

回调函数接收第i中指定的作为参数的模块列表中的所有模块的的export作为函数参数，并且顺序和该列表中的模块顺序一致。

1. If requested module cannot be returned, the       callback should receive null correspondingly.

如果请求的模块没有任何返回，回调函数也必须相应的按照顺序接收null。

The exports Object

In a module, there is a free variable called "exports", that is an object that the module may add its API to as it executes.

在模块中，还有一个参数“exports”，exports是一个对象，包含这个模块的所有API。

The module Object

1. module.uri

The full resolved uri to the module.

模块的完整可解析的uri

1. module.dependencies

A list of module identifiers that required by the module.

模块依赖的其他模块标识列表

1. module.exports

The exported API of the module. It is the same as exports object.

模块公开的export对象。

Module Identifier

1. A module identifier is and must be a literal      string.

模块标识必须是合法的字符串

1. Module identifiers may not have a filename      extensions like .js.

模块标识不能包含文件扩展名，如.js

1. Module identifiers should be dash-joined string,      such as foo-bar.

模块标识可以使用“-”连接，如foo-bar

1. Module identifiers can be a relative path, like ./foo and ../bar.

模块标识可以使用相对路径，如 ./foo、../bar

Sample Code

A typical sample

math.js

define(function(require, exports, module) {

exports.add = function() {

var sum = 0, i = 0, args = arguments, l = args.length;

while (i < l) {

sum += args[i++];

}

return sum;

};

});

increment.js

define(function(require, exports, module) {

var add = require('math').add;

exports.increment = function(val) {

return add(val, 1);

};

});

program.js

define(function(require, exports, module) {

var inc = require('increment').increment;

var a = 1;

inc(a); // 2

module.id == "program";

});

Wrapped modules with non-function factory

object-data.js

define({

foo: "bar"

});

array-data.js

define([

'foo',

'bar'

]);

string-data.js

define('foo bar');

------------------------------------------------

来源：

https://github.com/cmdjs/specification/blob/master/draft/module.md

扩展：

https://github.com/seajs/seajs/issues/242