Require

This touches both the module system and how Node’s runtime process loads code. Let’s break it down 👇

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📦 What is require?

• require is a built-in function in Node.js used to import modules.

• A module can be:

  • A built-in Node module (e.g., fs, http)

  • A third-party module (from node_modules, installed via npm/yarn)

  • A local file module (./myFile.js)

Example:

const fs = require("fs");        // built-in
const express = require("express"); // npm package
const myUtils = require("./utils"); // local file

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⚙️ How does require work in the process?

When you call require(...), Node.js goes through these steps internally:

1. Resolve

   • Node figures out what file or module you’re asking for.

   • Checks in order:

     • Is it a core (built-in) module like fs?

     • Is it in node_modules?

     • Is it a relative/absolute path?

2. Load

   • Reads the file (if it’s a .js, .json, or .node file).

   • If .json, it parses it.

   • If .js, it runs the file inside Node’s module wrapper (see below).

3. Wrap

   • Node wraps each file in a function for encapsulation:

     (function(exports, require, module, __filename, __dirname) {
       // your code here
     });

   • That’s why every file has access to require, module, exports, __dirname, and __filename without you declaring them.

4. Execute

   • Runs the module code in the current process.

5. Cache

   • The result (module.exports) is stored in require.cache.

   • If you require the same file again, Node won’t reload it — it just returns the cached version (for efficiency).

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🧠 So, in terms of the Node process:

• require is not part of JavaScript itself — it’s part of Node’s module loader system.

• It’s tied into the current process:

  • Resolves modules relative to the process’s cwd() or the requiring file.

  • Loads and executes code inside the process.

  • Caches modules so the process doesn’t re-execute them unnecessarily.

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✅ In short:
require is the function that the Node process uses to resolve, load, and cache modules. It runs your files inside a special wrapper, which is why globals like __dirname, module, and exports exist.