load(url, context, nextLoad)

加载器 API 正在重新设计。 这个钩子可能会消失，或者它的签名可能会改变。 不要依赖下面描述的 API。

在此 API 的先前版本中，它被拆分为 3 个单独的、现已弃用的钩子（getFormat、getSource 和 transformSource）。

• url <string> resolve 链返回的 URL
• context <Object>
  • conditions <string[]> 相关 package.json 的导出条件
  • format <string> | <null> | <undefined> resolve 钩子链可选提供的格式
  • importAssertions <Object>
• nextLoad <Function> 链中后续的 load 钩子，或者用户提供的最后一个 load 钩子之后的 Node.js 默认 load 钩子
  • specifier <string>
  • context <Object>
• 返回: <Object>
  • format <string>
  • shortCircuit <undefined> | <boolean> 此钩子打算终止 resolve 钩子链的信号。 默认值: false
  • source <string> | <ArrayBuffer> | <TypedArray> Node.js 评估的来源

load 钩子提供了一种方式来定义确定网址应如何解释、检索、以及解析的自定义方法。 它还负责验证导入断言。

format 的最终值必须是以下之一：

source 的值对于类型 'builtin' 被忽略，因为目前无法替换 Node.js 内置（核心）模块的值。 source 的值对于类型 'commonjs' 被忽略，因为 CommonJS 模块加载器没有为 ES 模块加载器提供覆盖 CommonJS 模块返回值 的机制。 这个限制将来可能会被克服。

警告：ESM load 钩子和来自 CommonJS 模块的命名空间导出不兼容。 尝试将它们一起使用将导致导入中的空对象。 这可能会在未来得到解决。

这些类型都对应于 ECMAScript 中定义的类。

• 特定的 ArrayBuffer 对象是 SharedArrayBuffer。
• 特定的 TypedArray 对象是 Uint8Array。

如果基于文本的格式（即 'json'、'module'）的源值不是字符串，则使用 util.TextDecoder 将其转换为字符串。

load 钩子提供了一种方法来定义用于检索 ES 模块说明符的源代码的自定义方法。 这将允许加载器潜在地避免从磁盘读取文件。 它还可以用于将无法识别的格式映射到支持的格式，例如 yaml 到 module。

export async function load(url, context, nextLoad) {
  const { format } = context;

  if (Math.random() > 0.5) { // 某些条件
    /*
      For some or all URLs, do some custom logic for retrieving the source.
      Always return an object of the form {
        format: <string>,
        source: <string|buffer>,
      }.
    */
    return {
      format,
      shortCircuit: true,
      source: '...',
    };
  }

  // 推迟到链中的下一个钩子。
  return nextLoad(url);
}

在更高级的场景中，这也可用于将不受支持的源转换为受支持的源（请参阅下面的示例）。

The loaders API is being redesigned. This hook may disappear or its signature may change. Do not rely on the API described below.

In a previous version of this API, this was split across 3 separate, now deprecated, hooks (getFormat, getSource, and transformSource).

• url <string> The URL returned by the resolve chain
• context <Object>
  • conditions <string[]> Export conditions of the relevant package.json
  • format <string> | <null> | <undefined> The format optionally supplied by the resolve hook chain
  • importAssertions <Object>
• nextLoad <Function> The subsequent load hook in the chain, or the Node.js default load hook after the last user-supplied load hook
  • specifier <string>
  • context <Object>
• Returns: <Object>
  • format <string>
  • shortCircuit <undefined> | <boolean> A signal that this hook intends to terminate the chain of resolve hooks. Default: false
  • source <string> | <ArrayBuffer> | <TypedArray> The source for Node.js to evaluate

The load hook provides a way to define a custom method of determining how a URL should be interpreted, retrieved, and parsed. It is also in charge of validating the import assertion.

The final value of format must be one of the following:

The value of source is ignored for type 'builtin' because currently it is not possible to replace the value of a Node.js builtin (core) module. The value of source is ignored for type 'commonjs' because the CommonJS module loader does not provide a mechanism for the ES module loader to override the CommonJS module return value. This limitation might be overcome in the future.

Caveat: The ESM load hook and namespaced exports from CommonJS modules are incompatible. Attempting to use them together will result in an empty object from the import. This may be addressed in the future.

These types all correspond to classes defined in ECMAScript.

• The specific ArrayBuffer object is a SharedArrayBuffer.
• The specific TypedArray object is a Uint8Array.

If the source value of a text-based format (i.e., 'json', 'module') is not a string, it is converted to a string using util.TextDecoder.

The load hook provides a way to define a custom method for retrieving the source code of an ES module specifier. This would allow a loader to potentially avoid reading files from disk. It could also be used to map an unrecognized format to a supported one, for example yaml to module.

export async function load(url, context, nextLoad) {
  const { format } = context;

  if (Math.random() > 0.5) { // Some condition
    /*
      For some or all URLs, do some custom logic for retrieving the source.
      Always return an object of the form {
        format: <string>,
        source: <string|buffer>,
      }.
    */
    return {
      format,
      shortCircuit: true,
      source: '...',
    };
  }

  // Defer to the next hook in the chain.
  return nextLoad(url);
}

In a more advanced scenario, this can also be used to transform an unsupported source to a supported one (see Examples below).