close#1436
BREAKING CHANGE: When building a js/ts entry file with --target lib, the
library now exposes a Module with both default and named exports. This means
in the UMD build, the default export now needs to be accessed as
`window.yourLib.default`, and in the CommonJS build as
`const yourLib = require('yourLib').default`. If you don't have named exports
and want to retain the previous behavior, you can configure webpack to use
`output.libraryExport: 'default'` in `vue.config.js`.