24 es6-模块化陷阱

网易春招面试题

下面的代码输出什么

//counter.js
let counter=10
export default counter
//index.js
import mycounter from './counter'
mycounter+=1
console.log(mycounter)
//会报错
//但是如果吧mycounter注释掉，则会输出10
//mycounter=mycounter+1 右边的mycounter是10，左边的mycounter没有定义，报错
//若改为var mycounter=mycounter+1
//会输出NaN