Modules

Back in the earliest days of JavaScript - when it was but a wee browser-only language that looked like bastardized Java - JavaScript files were small. A callback here, a dynamic element there, and a sprinkle of (gasp) jQuery to make it all work.

But as the web has grown, we're not just shipping a bit of interactivity to static HTML pages anymore. We're building full-fledged applications with crazy amounts of state, logic, and dependencies. In the case of single page applications, sometimes HTML is just a shell that gets filled in with JavaScript at runtime.

Long story short, JS needed modules. In Go, you have packages. In Python, you have modules. Now, JavaScript also has modules - they're just a way to split your code into separate files and import the code you need across a large codebase.

Modules in JavaScript exist at the file level, just like Python. So, if you have a file called math.js that looks like this:

// math.js
const add = (a, b) => a + b;
const subtract = (a, b) => a - b;

module.exports = {
  add,
  subtract,
};

You can import and use those functions in another file like this:

// main.js
const { add, subtract } = require("./math.js");

console.log(add(1, 2)); // 3
console.log(subtract(1, 2)); // -1

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