What is an ESM module?

ESMs (ECMAScript modules) are the official standard format to package JavaScript code for reuse. Modules are defined using import and export statements. 1

Default exports in ESM

The way we export "things" from our libraries impacts the way they can get imported by clients of our libraries.

For example, if we define a module and export cheese from it as the default export:

export default cheese;
// same as `export { cheese as default };`

Then clients of our library should import it like this:

import cheese from 'my-library';

But had we defined cheese as a non-default export:

export cheese;

Then we should have used a different syntax to import it:

import { cheese } from 'my-library';

• #javascript
• #typescript