A simple implementation of CLS under Node.js

cls.js

const {
  executionAsyncId,
  createHook,
} = require("async_hooks");

const { writeSync: fsWrite } = require("fs");
const log = (...args) => fsWrite(1, `${args.join(" ")}\n`);

const Storage = {};
Storage[executionAsyncId()] = {};

createHook({
  init(asyncId, _type, triggerId, _resource) {
    // log(asyncId, Storage[asyncId]);
    Storage[asyncId] = {};
    if (Storage[triggerId]) {
      Storage[asyncId] = { ...Storage[triggerId] };
    }
  },
  after(asyncId) {
    delete Storage[asyncId];
  },
  destroy(asyncId) {
    delete Storage[asyncId];
  },
}).enable();

class CLS {
  static get(key) {
    return Storage[executionAsyncId()][key];
  }
  static set(key, value) {
    Storage[executionAsyncId()][key] = value;
  }
}


// --- seperate line ---

function timeout(id) {
  CLS.set('a', id)
  setTimeout(() => {
    const a = CLS.get('a')
    console.log(a)
  }, Math.random() * 1000);
}

timeout(1)
timeout(2)
timeout(3)