JavaScript Quiz: Modules

Which file extension does Node.js require for ECMAScript module files?

.mjs

Define two classes in a module, and export them (so they can be used in other modules).

export class ExportMe1 { 
    greet() { console.log("Hello 1"); }
}

export class ExportMe2 { 
    greet() { console.log("Hello 2"); }
}

// alternative to using the "export" keyword above:
// export { ExportMe1, ExportMe2 };

Explicitly import & use the two classes that were exported above.

import { ExportMe1, ExportMe2 } from "./exports.mjs";

new ExportMe1().greet();
new ExportMe2().greet();

Explicitly import & use the two classes that were exported above, but with import aliases.

import { ExportMe1 as Ex1, ExportMe2 as Ex2} from "./exports.mjs";

new Ex1().greet();
new Ex2().greet();

Implicitly import & use the two classes that were exported above.

import * as Imported from "./exports.mjs";

new Imported.ExportMe1().greet();
new Imported.ExportMe2().greet();

Define a class in a module as default export (so it can be used in other modules).

// there can be only one default export per module
export default class ExportMe3 {
    greet() { console.log("Hello 3"); }
}

Explicitly import & use the class that was default-exported above.

// importing default exports doesn't need curly braces, 
// and can be aliased on-the-fly without "as" syntax:
import Ex3 from "./exports-default.mjs";
new Ex3().greet();