ES6+ javascript module export options
A year and some later, here is the best information I've found on the subject.
There are 4 types of exports. Here are usage examples of each, along with some imports that use them:
Export Syntax
// default exports
export default 42;
export default {};
export default [];
export default (1 + 2);
export default foo;
export default function () {}
export default class {}
export default function foo () {}
export default class foo {}
// variables exports
export var foo = 1;
export var foo = function () {};
export var bar;
export let foo = 2;
export let bar;
export const foo = 3;
export function foo () {}
export class foo {}
// named exports
export {};
export {foo};
export {foo, bar};
export {foo as bar};
export {foo as default};
export {foo as default, bar};
// exports from
export * from "foo";
export {} from "foo";
export {foo} from "foo";
export {foo, bar} from "foo";
export {foo as bar} from "foo";
export {foo as default} from "foo";
export {foo as default, bar} from "foo";
export {default} from "foo";
export {default as foo} from "foo";
Import Syntax
// default imports
import foo from "foo";
import {default as foo} from "foo";
// named imports
import {} from "foo";
import {bar} from "foo";
import {bar, baz} from "foo";
import {bar as baz} from "foo";
import {bar as baz, xyz} from "foo";
// glob imports
import * as foo from "foo";
// mixing imports
import foo, {baz as xyz} from "foo";
import foo, * as bar from "foo";
// just import
import "foo";
Source.
Both of these are valid.
Method 1 provides named exports. The key here is that you can export more than one thing. This should be used instead of exporting an object with multiple properties. When you import a module with named exports, use import {a, b} from c.
Method 2 provides the default export. There can be only one default export. This is primarily used when you are exporting a single thing, like a class, or a single function that you expect to be used without any additional support. When you import a module with a default export, use import d from c.
Note that you can use both! so if you have a major, primary function with a handful of occasionally used helpers, you can export the helpers, and export default the primary. When you import a module and need both kinds of exports, use import d, {a, b} from c.
One other option is that you can get named exports by listing them at the end of your module, like so: export {a,b,c}. You can also rename them export {a as $a, b as c}.
I got all of this from this article, which is the best source for up-to-date es6 module information that I've been able to find.
- Are both of these valid?
No, export function () { return answer; }; is invalid, either you use default, or you add a name to that function declaration.
- If so, why do they both exist?
They don't :)
- Are there other valid options for module exports using ES6 syntax?
You can see a lot of valid options here: https://github.com/eslint/espree/pull/43