In JavaScript we can separate a program into separate files. How do we make the functions we define in a file available to other files?

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 }

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'