Function addBuiltinLibsToObject

lib/internal/modules/helpers.js:264–321

* Add built-in modules to a global or REPL scope object. * @param {Record } object - The object such as `globalThis` to add the built-in modules to. * @param {string} dummyModuleName - The label representing the set of built-in modules to add.

(object, dummyModuleName)

 * @param {string} dummyModuleName - The label representing the set of built-in modules to add.
 */
function addBuiltinLibsToObject(object, dummyModuleName) {
  // Make built-in modules available directly (loaded lazily).
  const Module = require('internal/modules/cjs/loader').Module;
  const { builtinModules } = Module;

  // To require built-in modules in user-land and ignore modules whose
  // `canBeRequiredByUsers` is false. So we create a dummy module object and not
  // use `require()` directly.
  const dummyModule = new Module(dummyModuleName);

  ArrayPrototypeForEach(builtinModules, (name) => {
    // Neither add underscored modules, nor ones that contain slashes (e.g.,
    // 'fs/promises') or ones that are already defined.
    if (name[0] === '_' ||
        StringPrototypeIncludes(name, '/') ||
        ObjectPrototypeHasOwnProperty(object, name)) {
      return;
    }
    // Goals of this mechanism are:
    // - Lazy loading of built-in modules
    // - Having all built-in modules available as non-enumerable properties
    // - Allowing the user to re-assign these variables as if there were no
    //   pre-existing globals with the same name.

    const setReal = (val) => {
      // Deleting the property before re-assigning it disables the
      // getter/setter mechanism.
      delete object[name];
      object[name] = val;
    };

    ObjectDefineProperty(object, name, {
      __proto__: null,
      get: () => {
        const lib = dummyModule.require(name);

        try {
          // Override the current getter/setter and set up a new
          // non-enumerable property.
          ObjectDefineProperty(object, name, {
            __proto__: null,
            get: () => lib,
            set: setReal,
            configurable: true,
            enumerable: false,
          });
        } catch {
          // If the property is no longer configurable, ignore the error.
        }

        return lib;
      },
      set: setReal,
      configurable: true,
      enumerable: false,
    });
  });
}