@theinternetfolks/context

Library to help you create a context that can be used to reference data, without prop drilling, in Node-based environments.

The inspiration comes from the concept of Context in React.

Prop drilling is the process of getting data from component A to component Z by passing it through multiple layers of intermediary React components. Instead of manually passing props down, Context provides a way to share values between components.

Passing data to child functions in Node-based environments is a challenge. You could use a static class that works as your storage, but in cases where the application might be accessed in parallel, this approach fails. There is a definite need for a context-like concept.

Instead of doing this:

callFunction1(originalData) {
    callFunction2(someData, originalData);
}

callFunction2(someData, originalData) {
    processOtherDataToo(someData);
    callFunction3(originalData);
}

callFunction3(originalData) {
    callFunction4(originalData);
}

callFunction4(originalData) {
    useTheOriginalDataFinally(originalData);
}

You can do this:

callFunction1(originalData) {
    Context.set(originalData);
    callFunction2(someData);
}

callFunction2(someData) {
    processOtherDataToo(someData);
    callFunction3();
}

callFunction3() {
    callFunction4();
}

callFunction4() {
    const data = Context.get();
    useTheOriginalDataFinally(data);
}

The library uses Async Local Storage internally, which provides an API to track the lifetime of asynchronous resources in a Node application.

Installation

Install with npm:

npm install @theinternetfolks/context

Install with pnpm:

pnpm add @theinternetfolks/context

Install with bun:

bun add @theinternetfolks/context

Install with yarn:

yarn add @theinternetfolks/context

Features

• Lightweight implementation using native AsyncLocalStorage
• TypeScript typings with interfaces support
• Works with all kinds of async functions (Promises, Timeouts, TCPWrap, UDP, etc.)

Usage/Examples

Example 1: Simple Function Call

const { Context } = require("@theinternetfolks/context");

const SomeFunction = () => {
  const data = Context.get();
  console.log(`Name: ${data.name}`);
};

(() => {
  Context.init(); // initialize the context for this run
  Context.set({ name: "The Internet Folks" });
  SomeFunction();
})();

Output:

Name: The Internet Folks

Example 2: Parent-Child Function Calls

const { Context } = require("@theinternetfolks/context");

const ChildFunction = () => {
  const data = Context.get();
  console.log(`Name from Context: ${data.name} in Child`);
};

const ParentFunction = () => {
  const data = Context.get();
  console.log(`Name from Context: ${data.name} in Parent`);
  ChildFunction();
};

(() => {
  Context.init(); // initialize the context for this run
  Context.set({ name: "The Internet Folks" });
  ParentFunction();
})();

Example 3: Usage in Express.js (Per-Request Context)

const express = require("express");
const { Context } = require("@theinternetfolks/context");

const app = express();

app.use(express.json());

app.use((req, res, next) => {
  Context.init(); // initialize the context for the request
  Context.set({ host: req.get("host") });
  next();
});

app.get("/", (req, res) => {
  const data = Context.get();
  return res.json({ host: data?.host });
});

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

Example 4: Express.js with TypeScript

import express from "express";
import { Context } from "@theinternetfolks/context";

interface IPayload {
    host: string;
}

const app = express();

app.use(express.json());

app.use((req, res, next) => {
  Context.init(); // initialize the context for the request
  Context.set({ host: req.get("host") });
  next();
});

app.get("/", (req, res) => {
  const context = Context.get<IPayload>();

  setTimeout(() => {
    console.log(context?.host);
  }, 2500);

  return res.json({ host: context?.host });
});

app.listen(6174, () => {
  console.log("Server running on port 6174");
});

Documentation

API Methods

• static init(): void; Initializes a new context. This must be called before setting data.

• static get<T>(key?: string | null): T; Retrieves the stored data in the context.

• static set(data: Record<string, any>): boolean; Stores data in the context.

• static remove(key?: string): void; Deletes the data stored in the context.

• static run<T>(fn: () => T | Promise<T>, initialData?: Record<string, any>): T | Promise<T>; Runs a function with an isolated context.

Tests

• Uses Bun Test Suite for unit testing.
• Load tested with k6 to ensure no data leakage across requests.

Test Coverage

Authors

• Sameer Khan (@monkfromearth)

Careers at The Internet Folks

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