Modules

A real program isn't one giant file. Node's module system — require() to pull code in, module.exports to make it available — is how you split logic across files and reuse it.

Exporting from a module

Whatever you attach to module.exports is what another file gets back when it requires this one:

function add(a, b) {
  return a + b;
}

function multiply(a, b) {
  return a * b;
}

module.exports = { add, multiply };

Requiring a module

const math = require("./math");

console.log(math.add(2, 3));
console.log(math.multiply(4, 5));

node index.js

5
20

The ./ in front of ./math is what tells Node this is a local file rather than an installed package — require("./math") resolves to math.js in the same folder, and the .js extension can be left off.

Requiring built-in and third-party modules

Node's own built-in modules and anything installed via npm are required by name, with no ./:

const path = require("path");

console.log(path.join("folder", "file.txt"));

folder/file.txt