I have a node.js library lib written in ES6 (compiled with Babel) in which I export the following submodules:
"use strict";
import * as _config from './config';
import * as _db from './db';
import * as _storage from './storage';
export var config = _config;
export var db = _db;
export var storage = _storage;
If from my main project I include the library like this
import * as lib from 'lib';
console.log(lib);
I can see the proper output and it work as expected { config: ... }. However, if I try to include the library like this:
import lib from 'lib';
console.log(lib);
it will be undefined.
Can someone explain what is happening here? Aren't the two import methods supposed to be equivalent? If not, what difference am I missing?
import * as lib from 'lib';
is asking for an object with all of the named exports of 'lib'.
export var config = _config;
export var db = _db;
export var storage = _storage;
are named exports, which is why you end up with an object like you did.
import lib from 'lib';
is asking for the default export of lib.
e.g.
export default 4;
would make lib === 4. It does not fetch the named exports. To get an object from the default export, you'd have to explicitly do
export default {
config: _config,
db: _db,
storage: _storage
};
Just adding to Logan's solution because understanding import with brackets, * and without solved a problem for me.
import * as lib from 'lib';
is the equivalent of:
import {config, db, storage} as lib from 'lib';
Where the * is similar to a wildcard that imports all of the export var from lib.
export var config;
export var db;
export var storage;
Alternatively, using:
import lib from 'lib';
Allows you to only access the default export:
// lib.js
export default storage;
Using {} also only imports specific components from the module, which reduces the footprint with bundlers like Webpack.
While:
import storage, { config, db } from './lib'
would import all modules including export default storage;
See Dan Abramov's answer: When should I use curly braces for ES6 import?
import X from Y; is a syntax sugar.
import lib from 'lib';
is equal to
import { default as lib } from 'lib';