使用名称来引用包

在一个包中，在包的 package.json "exports" 字段中定义的值可以通过包的名称引用。 例如，假设 package.json 是：

// package.json
{
  "name": "a-package",
  "exports": {
    ".": "./main.mjs",
    "./foo": "./foo.js"
  }
}

然后该包中的任何模块都可以引用包本身中的导出：

// ./a-module.mjs
import { something } from 'a-package'; // 从 ./main.mjs 导入 "something"。

自引用仅在 package.json 具有 "exports" 时可用，并且只允许导入 "exports"（在 package.json 中）允许的内容。 所以下面的代码，给定前面的包，会产生运行时错误：

// ./another-module.mjs

// 从 ./m.mjs 导入 "another"。
// 失败，因为 "package.json" "exports" 字段 
// 不提供名为 "./m.mjs" 的导出。
import { another } from 'a-package/m.mjs';

在 ES 模块和 CommonJS 模块中使用 require 时也可以使用自引用。 例如，这段代码也可以工作：

// ./a-module.js
const { something } = require('a-package/foo'); // 从 ./foo.js 加载。

最后，自引用也适用于作用域包。 例如，这段代码也可以工作：

// package.json
{
  "name": "@my/package",
  "exports": "./index.js"
}

// ./index.js
module.exports = 42;

// ./other.js
console.log(require('@my/package'));

$ node other.js
42

Within a package, the values defined in the package’s package.json "exports" field can be referenced via the package’s name. For example, assuming the package.json is:

// package.json
{
  "name": "a-package",
  "exports": {
    ".": "./main.mjs",
    "./foo": "./foo.js"
  }
}

Then any module in that package can reference an export in the package itself:

// ./a-module.mjs
import { something } from 'a-package'; // Imports "something" from ./main.mjs.

Self-referencing is available only if package.json has "exports", and will allow importing only what that "exports" (in the package.json) allows. So the code below, given the previous package, will generate a runtime error:

// ./another-module.mjs

// Imports "another" from ./m.mjs. Fails because
// the "package.json" "exports" field
// does not provide an export named "./m.mjs".
import { another } from 'a-package/m.mjs';

Self-referencing is also available when using require, both in an ES module, and in a CommonJS one. For example, this code will also work:

// ./a-module.js
const { something } = require('a-package/foo'); // Loads from ./foo.js.

Finally, self-referencing also works with scoped packages. For example, this code will also work:

// package.json
{
  "name": "@my/package",
  "exports": "./index.js"
}

// ./index.js
module.exports = 42;

// ./other.js
console.log(require('@my/package'));

$ node other.js
42