Side effects

In ES modules, side effects are "things that happen" in the module automatically, without the need for the developer to explicitly run a function.

ES modules don't need to have an export, and when you import a module, you don't have to access any exports if it has them. Anything that runs as part of the imported file will run automatically when imported.

// sayHi.js
function sayHi () {
	console.log('Hello there!');
}

// Run on init
sayHi();

// "Hello there!" will be automatically logged 
import './sayHi.js';