为什么npm在package.json中添加一些带下划线的属性

当我执行npm install koa-compose ，npm会自动添加一些带下划线的属性，他们有什么作用？ 喜欢这个：

 { "_args": [ [ "koa-compose", "/Users/keenwon/Desktop/demo" ] ], "_from": "koa-compose@latest", "_id": "koa-compose@2.4.0", "_inCache": true, "_installable": true, "_location": "/koa-compose", "_nodeVersion": "5.7.0", "_npmVersion": "3.7.5", "_phantomChildren": {}, "_spec": "koa-compose", "_where": "/Users/keenwon/Desktop/demo" "version": "2.4.0" }