index.js

const zones = Object.create(null);
let current;

const asyncHooks = require("async_hooks");
const asyncHook = asyncHooks.createHook({
  init(uid) {
    zones[uid] = current;
  },

  before(uid) {
    current = zones[uid];

    // it appears `init` is not called when using the `cluster` module,
    // therefore `zones[uid]` might not exist in `before`
    //
    // Work-around: set the current zone to the root zone, it's incorrect but it
    // allows using root data and create new zones by forking.
    //
    // see https://github.com/JsCommunity/node-zone/issues/3
    if (current === undefined) {
      current = root;
    }
  },

  destroy(uid) {
    delete zones[uid];
  },
});
asyncHook.enable();

class Zone {
  constructor(parent, spec) {
    if (parent === null) {
      // root zone
      this._data = Object.create(null);
      this._name = "<root>";
      this._parent = null;
    } else {
      const data = (this._data = Object.create(parent.data));
      this._parent = parent;

      let name;
      if (typeof spec === "string") {
        name = spec;
      } else if (spec != null) {
        name = spec.name;

        const { properties } = spec;
        if (properties) {
          for (const key in properties) {
            data[key] = properties[key];
          }
        }
      }

      this._name = name || `${parent.name} child`;
    }
  }

  get data() {
    return this._data;
  }

  get name() {
    return this._name;
  }

  get parent() {
    return this._parent;
  }

  fork(spec) {
    return new Zone(this, spec);
  }

  run(callback, thisArg, args) {
    const previous = current;
    try {
      current = this;
      return callback.apply(thisArg, args);
    } finally {
      current = previous;
    }
  }

  wrap(callback) {
    const zone = this;
    return function(...args) {
      return zone.run(callback, this, args);
    };
  }

  // minimal zone.js compatibility

  get(key) {
    return this._data[key];
  }

  getZoneWith(key) {
    if (Object.prototype.hasOwnProperty.call(this._data, key)) {
      return this;
    }

    const parent = this._parent;
    return parent && parent.getZoneWith(key);
  }
}

const root = (current = new Zone(null));

module.exports = {
  get current() {
    return current;
  },
};