JavaScript, how to export multiple functions

To export multiple functions from a JavaScript file, you use a named export: list the functions in curly braces after the export keyword. Other files can then import all of them, or just the ones they need.

This is how we split a program into separate files. Each file keeps its functions private until we explicitly export them.

You typically write a few functions, like this:

function sum(a, b) {
  return a + b
}

function mul(a, b) {
  return a * b
}

and you can make them available for any other file using this syntax:

export { sum, mul }

I like this style because the export list at the bottom acts as a summary of the file’s public interface.

The files that need the functionality exported will import all the functions, or just the ones they need:

import { sum, mul } from 'myfile'
import { mul } from 'myfile'

In a real project the path is usually relative, like './myfile.js'.

Exporting inline

Alternatively, you can put export directly in front of each function declaration:

export function sum(a, b) {
  return a + b
}

export function mul(a, b) {
  return a * b
}

The result is the same. Pick one style and stick with it in a codebase.

Renaming on import

Named imports must match the exported names. If a name clashes with something you already have, rename it with as:

import { sum as addNumbers } from './myfile.js'

addNumbers(1, 2) //3

You can also rename on the export side, with export { sum as add }.

Mixing with a default export

A file can have many named exports, but only one default export. You can combine them:

export default sum
export { mul }

and import both in one line:

import sum, { mul } from './myfile.js'

A common pitfall

The export keyword only works in ES modules. If you run a file like this with Node and it’s treated as CommonJS, you’ll get SyntaxError: Unexpected token 'export'.

The fix is to add "type": "module" to your package.json, or rename the file to use the .mjs extension. In the browser, load the file with <script type="module">.