在Babel 6.x中无法require（）默认导出值

问题描述

限时删除！！

app.js

  export default function（）{} 
  

index.js

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

然后，我可以运行 node index.js 没有错误。但是，使用Babel 6.x，运行以下代码

index.es6.js

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

导致错误

我想知道为什么？

解决方案

TL; DR

p>

  require（'./ app'）。 
  

说明

Babel 5曾经有 export default 的兼容性黑客：如果一个模块只包含一个导出，并且它是默认导出，则它被分配给 module.exports 。因此，例如，您的模块 app.js

  export default function（）{} 
  

将被转载到这个

 使用严格; 
 
 Object.defineProperty（exports，__esModule，{
 value：true 
}）; 
 
 exports [default] = function（）{}; 
 
 module.exports = exports [default]; 
  

纯粹完成以兼容 require Babel-transpiled模块（就像你在做）。也是不一致的如果一个模块包含命名和默认导出，它不能是 require -d。

在现实中，对于ES6模块规范，与名称为 default 的命名导出相比，默认导出为不同。它只是语法糖，可以在编译时静态解决，所以这个

 从'./app'导入一些东西。 
  

与此相同

<$ p $从./app中导入{default}作为某个东西} p> 就是说，看来Babel 6决定放弃模块的互操作性。现在，您的模块 app.js 被转载为

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

如你所见，没有更多的赋值给 module.exports 。要需要这个模块，你需要做

  require（'。 /应用）的默认（）; 
  

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

I want to know why?

解决方案

TL;DR

You have to use

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

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

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

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