typeof一个模块都是undefined，new构造函数提示not defined

[Simon Lin]

模块lib/socket-connection.js：

module.exports = function SocketConnection () {}

引入：

import { SocketConnection } from 'xxx'

console.log(typeof SocketConnection) // undefined
console.log(SocketConnection) // function SocketConnection () {}

SocketConnection() // 正常执行函数
new SocketConnection() // Uncaught ReferenceError: SocketConnection is not defined