resolve(specifier, context, defaultResolve)

resolve 钩子返回给定模块说明符和父 URL 的解析文件 URL，以及可选的格式（例如 'module'）作为对 load 钩子的提示。 如果指定了格式，则 load 钩子最终负责提供最终的 format 值（可以随意忽略 resolve 提供的提示）；如果 resolve 提供了 format，则需要自定义 load 钩子，即使只是通过 Node.js 默认 load 钩子的值。

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

• specifier <string>
• context <Object>
  • conditions <string[]>
  • importAssertions <Object>
  • parentURL <string> | <undefined>
• defaultResolve <Function> The Node.js default resolver.
• Returns: <Object>
  • format <string> | <null> | <undefined> 'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'
  • url <string> The absolute url to the import target (such as file://…)

The resolve hook returns the resolved file URL for a given module specifier and parent URL, and optionally its format (such as 'module') as a hint to the load hook. If a format is specified, the load hook is ultimately responsible for providing the final format value (and it is free to ignore the hint provided by resolve); if resolve provides a format, a custom load hook is required even if only to pass the value to the Node.js default load hook.

The module specifier is the string in an import statement or import() expression, and the parent URL is the URL of the module that imported this one, or undefined if this is the main entry point for the application.

The conditions property in context is an array of conditions for package exports conditions that apply to this resolution request. They can be used for looking up conditional mappings elsewhere or to modify the list when calling the default resolution logic.

The current package exports conditions are always in the context.conditions array passed into the hook. To guarantee default Node.js module specifier resolution behavior when calling defaultResolve, the context.conditions array passed to it must include all elements of the context.conditions array originally passed into the resolve hook.

/**
 * @param {string} specifier
 * @param {{
 *   conditions: string[],
 *   parentURL: string | undefined,
 * }} context
 * @param {Function} defaultResolve
 * @returns {Promise<{ url: string }>}
 */
export async function resolve(specifier, context, defaultResolve) {
  const { parentURL = null } = context;
  if (Math.random() > 0.5) { // Some condition.
    // For some or all specifiers, do some custom logic for resolving.
    // Always return an object of the form {url: <string>}.
    return {
      url: parentURL ?
        new URL(specifier, parentURL).href :
        new URL(specifier).href,
    };
  }
  if (Math.random() < 0.5) { // Another condition.
    // When calling `defaultResolve`, the arguments can be modified. In this
    // case it's adding another value for matching conditional exports.
    return defaultResolve(specifier, {
      ...context,
      conditions: [...context.conditions, 'another-condition'],
    });
  }
  // Defer to Node.js for all other specifiers.
  return defaultResolve(specifier, context, defaultResolve);
}