https://rcoedo.com/blog/2020/06/15/context-dependent-imports-using-cls-and-getters

context-dependent-imports-using-getters-and-cls-1.js

const { AsyncLocalStorage } = require("async_hooks");
const { v4: uuid } = require("uuid");

const defaultStore = new Map();
defaultStore.set("requestId", "not-in-a-request");

const context = new AsyncLocalStorage();
context.enterWith(defaultStore);

const middleware = (req, res, next) => {
  context.run(new Map(), () => {
    context.getStore().set("requestId", uuid());
    next();
  });
};

module.exports = {
  context,
  middleware,
};

context-dependent-imports-using-getters-and-cls-2.js

const express = require("express");
const ctx = require("./context.js");

const app = express();
app.use(ctx.middleware);

app.get("/", (req, res) => {
  const id = ctx.context.getStore().get("requestId");
  console.log(`[${id}] request received`);
  res.send("It works!");
});

const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Express server listening on port ${port}`));

context-dependent-imports-using-getters-and-cls-3.js

module.exports = {
  get requestId() {
    return context.getStore().get("requestId");
  },
  middleware,
};

context-dependent-imports-using-getters-and-cls-4.js

const express = require("express");
const ctx = require("./context.js");

const app = express();
app.use(ctx.middleware);

app.get("/", (req, res) => {
  console.log(`[${ctx.requestId}] request received`);
  res.send("It works!");
});

const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Express server listening on port ${port}`));

context-dependent-imports-using-getters-and-cls-5.js

const express = require("express");
const { middleware, requestId } = require("./context.js"); // Now we're destructuring the module here.

const app = express();
app.use(middleware);

app.get("/", (req, res) => {
  console.log(`[${requestId}] request received`); // We still use the requestId here.
  res.send("It works!");
});

const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Express server listening on port ${port}`));

Examples for "Context-Dependent Imports Using CLS and Getters"

This gist contains the examples for the article "Context-Dependent Imports Using CLS and Getters".

- https://medium.com/trabe/context-dependent-imports-using-cls-and-getters-71b97c1baf3c
- https://rcoedo.com/blog/2020/06/15/context-dependent-imports-using-cls-and-getters