node/lib/internal/loader/ModuleJob.js

'use strict';

const { ModuleWrap } = internalBinding('module_wrap');
const { SafeSet, SafePromise } = require('internal/safe_globals');
const assert = require('assert');
const resolvedPromise = SafePromise.resolve();

const enableDebug = (process.env.NODE_DEBUG || '').match(/\besm\b/) ||
    process.features.debug;

/* A ModuleJob tracks the loading of a single Module, and the ModuleJobs of
 * its dependencies, over time. */
class ModuleJob {
  // `loader` is the Loader instance used for loading dependencies.
  // `moduleProvider` is a function
  constructor(loader, url, moduleProvider) {
    this.loader = loader;
    this.error = null;
    this.hadError = false;

    // This is a Promise<{ module, reflect }>, whose fields will be copied
    // onto `this` by `link()` below once it has been resolved.
    this.modulePromise = moduleProvider(url);
    this.module = undefined;
    this.reflect = undefined;

    // Wait for the ModuleWrap instance being linked with all dependencies.
    const link = async () => {
      const dependencyJobs = [];
      ({ module: this.module,
         reflect: this.reflect } = await this.modulePromise);
      assert(this.module instanceof ModuleWrap);
      this.module.link(async (dependencySpecifier) => {
        const dependencyJobPromise =
            this.loader.getModuleJob(dependencySpecifier, url);
        dependencyJobs.push(dependencyJobPromise);
        const dependencyJob = await dependencyJobPromise;
        return (await dependencyJob.modulePromise).module;
      });
      if (enableDebug) {
        // Make sure all dependencies are entered into the list synchronously.
        Object.freeze(dependencyJobs);
      }
      return SafePromise.all(dependencyJobs);
    };
    // Promise for the list of all dependencyJobs.
    this.linked = link();

    // instantiated == deep dependency jobs wrappers instantiated,
    // module wrapper instantiated
    this.instantiated = undefined;
  }

  async instantiate() {
    if (this.instantiated) {
      return this.instantiated;
    }
    return this.instantiated = this._instantiate();
  }

  // This method instantiates the module associated with this job and its
  // entire dependency graph, i.e. creates all the module namespaces and the
  // exported/imported variables.
  async _instantiate() {
    const jobsInGraph = new SafeSet();

    const addJobsToDependencyGraph = async (moduleJob) => {
      if (jobsInGraph.has(moduleJob)) {
        return;
      }
      jobsInGraph.add(moduleJob);
      const dependencyJobs = await moduleJob.linked;
      return Promise.all(dependencyJobs.map(addJobsToDependencyGraph));
    };
    try {
      await addJobsToDependencyGraph(this);
    } catch (e) {
      if (!this.hadError) {
        this.error = e;
        this.hadError = true;
      }
      throw e;
    }
    this.module.instantiate();
    for (const dependencyJob of jobsInGraph) {
      // Calling `this.module.instantiate()` instantiates not only the
      // ModuleWrap in this module, but all modules in the graph.
      dependencyJob.instantiated = resolvedPromise;
    }
    return this.module;
  }

  async run() {
    const module = await this.instantiate();
    try {
      module.evaluate();
    } catch (e) {
      e.stack;
      this.hadError = true;
      this.error = e;
      throw e;
    }
    return module;
  }
}
Object.setPrototypeOf(ModuleJob.prototype, null);
module.exports = ModuleJob;