Class ModuleLoader

lib/internal/modules/esm/loader.js:138–857

* This class covers the base machinery of module loading. There are two types of loader hooks: * 1. Asynchronous loader hooks, which are run in a separate loader hook worker thread. * This is configured in #asyncLoaderHooks. * 2. Synchronous loader hooks, which are run in-thread. This is share

 *    stored in the cross-module syncResolveHooks and syncLoadHooks arrays.
 */
class ModuleLoader {
  /**
   * The conditions for resolving packages if `--conditions` is not used.
   */
  #defaultConditions = getDefaultConditions();

  /**
   * Registry of resolved specifiers
   */
  #resolveCache = new ResolveCache();

  /**
   * Registry of loaded modules, akin to `require.cache`
   */
  loadCache = new LoadCache();

  /**
   * @see {AsyncLoaderHooks.isForAsyncLoaderHookWorker}
   * Shortcut to this.#asyncLoaderHooks.isForAsyncLoaderHookWorker.
   */
  isForAsyncLoaderHookWorker = false;

  /**
   * Asynchronous loader hooks to pass requests to.
   *
   * Note that this value _MUST_ be set with `#setAsyncLoaderHooks`
   * because it needs to copy `#asyncLoaderHooks.isForAsyncLoaderHookWorker`
   * to this property.
   * TODO(joyeecheung): this was a legacy of the previous setup of import.meta.resolve
   * configuration; put this information in the environment directly instead.
   *
   * When the ModuleLoader is created on a loader hook thread, this is
   * {@link AsyncLoaderHooksOnLoaderHookWorker}, and its methods directly call out
   * to loader methods. Otherwise, this is {@link AsyncLoaderHooksProxiedToLoaderHookWorker},
   * and its methods post messages to the loader thread and possibly block on it.
   * @see {ModuleLoader.#setAsyncLoaderHooks}
   * @type {AsyncLoaderHooks}
   */
  #asyncLoaderHooks;

  constructor(asyncLoaderHooks) {
    this.#setAsyncLoaderHooks(asyncLoaderHooks);
  }

  /**
   * Change the currently activate async loader hooks for this module
   * loader to be the provided `AsyncLoaderHooks`.
   *
   * If present, this class customizes its core functionality to the
   * `AsyncLoaderHooks` object, including registration, loading, and resolving.
   * There are some responsibilities that this class _always_ takes
   * care of, like validating outputs, so that the AsyncLoaderHooks object
   * does not have to do so.
   *
   * Calling this function alters how modules are loaded and should be
   * invoked with care.
   * @param {AsyncLoaderHooks} asyncLoaderHooks
   */