ES modules

Learn ES module syntax with import and export.

What are ES modules?

ES modules are JavaScript's modern module system. They let you reuse code from one file in another. This is the recommended approach in Node.js 22.

To export something from a module, you use the export keyword; to import from another module, you use import. ESM is enabled with the .mjs extension or by setting "type": "module" in package.json.

This course uses ESM throughout.

import and export

To export a function, you write export at the start of its definition. For example, export function greet(name) { ... }.

To use this function in another file, you write import { greet } from './greet.js'. The curly braces specify the exported name; from links the file path.

This way, code is split into small pieces and becomes easier to maintain.

Exercise Export a function

Define a greet(name) function with export. The function should return the concatenation of 'Hello, ' and name. Then call console.log with greet('Alex').

Show example solution

export function greet(name) {
  return "Hello, " + name;
}

console.log(greet("Alex"));

Test yourself

Match the module concepts

import

Bring in
export

Send out
.mjs

ESM file extension
"type": "module"

Enable ESM

import syntax

____ { greet } from "./greet.js";

Show answer

import { greet } from "./greet.js";

What does export do?
- Deletes a value
- Makes a value available in other files
- Renames a value
- Hides a value
Show answer

Makes a value available in other files — export sends a value out.

Next lesson: package.json

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