ExpressJS: What is the difference between app.local and res.local?

Question

I'm trying to learn Express and in my app I have middleware that passes the session object from the Request object to my Response object so that I can access it in my views:

app.use((req, res, next) ->
  res.locals.session = req.session
  next()
)

But app.locals is available to the view as well right? So is it the same if I do app.locals.session = req.session? Is there a convention for the types of things app.locals and res.locals are used for?

I was also confused on what the difference is between res.render() and res.redirect()? When should each be used?

Thanks for reading. Any help related to Express is appreciated!

Answer 1

app.locals and res.locals can be used in different contexts.

res.locals is for when you handle the route where you have a res object, you won't have an app object there and vice-versa for app.locals.

also res.render will render the page, to handle the request. res.redirect will redirect them to a different page.

For example if they try to access /account without logging in, you could flash a message and use res.redirect('/login')

Answer 2

To illustrate this further, I remember viewing a flowchart which shows how express renders variables found inside a template. This is from "Node.js In Action." I recommend reading the chapter discussing Express.js.