Context for node/bun

async-hooks.ts

import { AsyncLocalStorage } from "node:async_hooks";

function createCtx<T>(name: string, defaultValue?: T) {
	const ctx = new AsyncLocalStorage<T>({ name });

	const set = (x: T) => ctx.enterWith(x);
	const maybeGet = () => ctx.getStore();
	const get = (): T => {
		const val = maybeGet();
		if (val === undefined) {
			throw new Error(`Missing required context value for ${name}`);
		}
		return val;
	};

	if (defaultValue !== undefined) {
		ctx.enterWith(defaultValue);
	}

	return { ctx, get, maybeGet, set };
}

type Logger = { info: (msg: string) => unknown };

const logger = createCtx<Logger>("LoggerCtx", {
	info(msg) {
		console.log(msg);
	},
});

logger.get().info("hi1");

logger.ctx.run({
	info(msg) {
		console.log("inside runner " + msg);
	},
}, () => {
	logger.get().info("hi2");
});

logger.get().info("hi3");

// Prints out:
// hi1
// inside runner hi2
// hi3