请教：nodeclub视图文件里的local是什么？

服务端：res.render('book/book',{bookInfo:bookinfo,authorInfo:authorinfo,bookChapter:bookchapter, bookSimiler:booksimiler,bookRecommends:bookrecommends});

web 页面： <% if(locals.bookInfo ) { %> <% } %>

这些都是自动的吗？我搜索代码没看到有如下类似的代码：

app.use(function(req, res, next){ res.locals.user = req.user; res.locals.authenticated = ! req.user.anonymous; next(); });

当然，我指的不仅仅是locals.user,代码中还有很多，比如：locals.edit_error...

相关链接： http://expressjs.com/3x/api.html#res.locals http://expressjs.com/3x/api.html#res.render https://github.com/cnodejs/nodeclub/blob/e41c067a7c6730fad89a8cb21ccc25264c44248d/middlewares/auth.js#L6