Difference between _locals and locals in express 4.0

问题

For some reason in my jade files I can access files set with _locals and not locals?:

app.use(function (req, res, next) {
    if(req.isAuthenticated()) //true
    {
        res.locals.user = req.user;
    }else {
        res.locals.user = null;
    }
}

Jade

-console.info(_locals.user); //{_id: 5775.....4343}
-console.info(locals.user); //undefined
-console.info(user); //null

来源：https://stackoverflow.com/questions/31253666/difference-between-locals-and-locals-in-express-4-0