Can't require() default export value in Babel 6.x

Question

In Babel 5.x, I can write the following code:

app.js

export default function (){} 

index.js

require('babel/register'); require('./app')(); 

Then, I can run node index.js with no errors. However, using Babel 6.x, running the following code

index.es6.js

require('babel-core/register'); require('./app')(); 

results in an error

require(...) is not a function

I want to know why?

Answer 1

TL;DR

You have to use

const app = require('./app').default; app(); 

Explanation

Babel 5 used to have a compatibility hack for export default: if a module contained only one export, and it was a default export, it was assigned to module.exports. So, for example, your module app.js

export default function () {} 

would be transpiled to this

"use strict";  Object.defineProperty(exports, "__esModule", {   value: true });  exports["default"] = function () {};  module.exports = exports["default"]; 

This was done purely for compatibility with require-ing Babel-transpiled modules (like you are doing). It was also inconsistent; if a module contained both named and default exports, it could not be require-d.

In reality, according to the ES6 module spec, a default export is no different than a named export with the name default. It is just syntactic sugar which can be statically resolved at compile time, so this

import something from './app'; 

is the same as this

import { default as something } from './app'; 

That being said, it appears that Babel 6 decided to drop the interoperability hack when transpiling modules. Now, your module app.js is transpiled as

'use strict';  Object.defineProperty(exports, "__esModule", {     value: true });  exports.default = function () {}; 

As you see, no more assignment to module.exports. To require this module, you need to do

const app = require('./app').default; app(); 

Or, more concisely, and closer to your original code:

require('./app').default(); 

Answer 2

Just to follow up with the correct answer above.

If you wanna use default export behavior of babel@5, you can try babel-plugin-add-module-exports plugin.

It's working pretty well for me.