How to create global variables accessible in all views using Express / Node.JS?

Question

Ok, so I have built a blog using Jekyll and you can define variables in a file _config.yml which are accessible in all of the templates/layouts. I am currently

Answer 1

After having a chance to study the Express 3 API Reference a bit more I discovered what I was looking for. Specifically the entries for app.locals and then a bit farther down res.locals held the answers I needed.

I discovered for myself that the function app.locals takes an object and stores all of its properties as global variables scoped to the application. These globals are passed as local variables to each view. The function res.locals, however, is scoped to the request and thus, response local variables are accessible only to the view(s) rendered during that particular request/response.

So for my case in my app.js what I did was add:

app.locals({
    site: {
        title: 'ExpressBootstrapEJS',
        description: 'A boilerplate for a simple web application with a Node.JS and Express backend, with an EJS template with using Twitter Bootstrap.'
    },
    author: {
        name: 'Cory Gross',
        contact: 'CoryG89@gmail.com'
    }
});

Then all of these variables are accessible in my views as site.title, site.description, author.name, author.contact.

I could also define local variables for each response to a request with res.locals, or simply pass variables like the page's title in as the optionsparameter in the render call.

EDIT: This method will not allow you to use these locals in your middleware. I actually did run into this as Pickels suggests in the comment below. In this case you will need to create a middleware function as such in his alternative (and appreciated) answer. Your middleware function will need to add them to res.locals for each response and then call next. This middleware function will need to be placed above any other middleware which needs to use these locals.

EDIT: Another difference between declaring locals via app.locals and res.locals is that with app.locals the variables are set a single time and persist throughout the life of the application. When you set locals with res.locals in your middleware, these are set everytime you get a request. You should basically prefer setting globals via app.locals unless the value depends on the request req variable passed into the middleware. If the value doesn't change then it will be more efficient for it to be set just once in app.locals.

Answer 2

You can do this by adding them to the locals object in a general middleware.

app.use(function (req, res, next) {
   res.locals = {
     siteTitle: "My Website's Title",
     pageTitle: "The Home Page",
     author: "Cory Gross",
     description: "My app's description",
   };
   next();
});

Locals is also a function which will extend the locals object rather than overwriting it. So the following works as well

res.locals({
  siteTitle: "My Website's Title",
  pageTitle: "The Home Page",
  author: "Cory Gross",
  description: "My app's description",
});

Full example

var app = express();

var middleware = {

    render: function (view) {
        return function (req, res, next) {
            res.render(view);
        }
    },

    globalLocals: function (req, res, next) {
        res.locals({ 
            siteTitle: "My Website's Title",
            pageTitle: "The Root Splash Page",
            author: "Cory Gross",
            description: "My app's description",
        });
        next();
    },

    index: function (req, res, next) {
        res.locals({
            indexSpecificData: someData
        });
        next();
    }

};


app.use(middleware.globalLocals);
app.get('/', middleware.index, middleware.render('home'));
app.get('/products', middleware.products, middleware.render('products'));

I also added a generic render middleware. This way you don't have to add res.render to each route which means you have better code reuse. Once you go down the reusable middleware route you'll notice you will have lots of building blocks which will speed up development tremendously.