AsyncLocalStorage MTC

index.mjs

import { withCounter, withContext, log } from "./util.mjs";

let delay = 200;

log("TOKEN");
withContext("abc123", () => {
	log("🅰️");
	setTimeout(() => {
		log("🅱️");
	}, delay * 2);
});

log("COUNTER");
withCounter(() => {
	log("1️⃣");
	setTimeout(() => {
		log("2️⃣");
	}, delay);
});

log("EOF");

util.mjs

import { AsyncLocalStorage } from "node:async_hooks";

let store = new AsyncLocalStorage();

export function withCounter(fn) {
	store.run({ count: 0 }, fn);
}

export function withContext(ctx, fn) {
	store.run(ctx, fn);
}

export function log(msg) {
	let ctx = store.getStore();
	if (Number.isInteger(ctx?.count)) {
		ctx.count++;
	}
	let prefix = msg.padEnd(10, " ")
	console.log(prefix, ctx ?? "missing context store");
}