CMD規範（通用模塊定義規範）（翻譯）

最近在使用sea.js。你們知道sea.js遵循CMD規範。該規範的英文說明很簡潔，我試着翻譯了一下，旨在交流。

Common Module Definition

通用模塊定義規範

 

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.

本規範規定如何定義和書寫執行在瀏覽器環境中的js模塊，這就是說，本規範定義了一個模塊的最小API，這些API提供與該模塊系統的交互。

• Modules are singletons.

模塊都是單例的。

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

模塊範圍內的自由變量不該該被引入。

• Execution must be lazy.

模塊的執行是按需執行的。

 

 

Module Definition

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

模塊是使用關鍵字「define」定義的一個函數。

define(factory);

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

factory.define函數接受一個參數，模塊工廠

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

Factory多是一個函數，或是一個可驗證值

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

若是factory是一個函數，若是參數指定了，這個函數的前三個參數，按照順序這三個參數是「require」，「exports」，「module」

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

若是factory不是一個函數，模塊的exports必須設置成一個對象。

Module Context

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

模塊中三個變量：require，exports和module

define(function(require, exports, module) {

 

  // The module code goes here

 

});

The require Function

1. require is      a function

require是一個函數

1. require accepts a module identifier.

require接受一個模塊標識

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

require返回一個外部模塊對外公開的API

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

若是請求的模塊沒有返回API，require必須返回null

2. require.async is a function require.async是一個函數
1. require.async accepts a list of module identifiers and a       optional callback function.

require.async接受一個模塊標識列表和一個回調函數

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

回調函數接收第i中指定的做爲參數的模塊列表中的全部模塊的的export做爲函數參數，而且順序和該列表中的模塊順序一致。

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

若是請求的模塊沒有任何返回，回調函數也必須相應的按照順序接收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.

在模塊中，還有一個參數「exports」，exports是一個對象，包含這個模塊的全部API。

The module Object

1. module.uri

The full resolved uri to the module.

模塊的完整可解析的uri

2. module.dependencies

A list of module identifiers that required by the module.

模塊依賴的其餘模塊標識列表

3. module.exports

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

模塊公開的export對象。

Module Identifier

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

模塊標識必須是合法的字符串

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

模塊標識不能包含文件擴展名，如.js

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

 模塊標識能夠使用「-」鏈接，如foo-bar

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

模塊標識能夠使用相對路徑，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');

 

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來源：

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

擴展：

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