JavaScript modules are reusable pieces of code that can be exported from one program and imported for use in another program.

Modules are particularly useful for a number of reasons. By separating code with similar logic into files called modules, we can:

• find, fix, and debug code more easily;
• reuse and recycle defined logic in different parts of our application;
• keep information private and protected from other modules;
• and, importantly, prevent pollution of the global namespace and potential naming collisions, by cautiously selecting variables and behavior we load into a program.

In this lesson, we’ll cover two ways to implement modules in JavaScript: Node.js’s module.exports and require() syntax, as well as the ES6 import/export syntax.