Creating Middleware Global vs local var

Question

During my research on how to better handle globally used data I found this Question See 2. Answer

So I integrated this approach into my code basis and came up with a problem, which i would like to discuss. Hope someone can help me here.

I created a new file middleware.jscontaining almost the same code as in the answer from SO, just with some small modifications:

const url = require('../db/url');

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

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

        index: async function (req, res, next) {
            res.locals = {
                index: "index2",
                loggedIn: req.user ? true : false,
                linkObj: await url.getAllUrl()
            };
            next();
        }
};

In my app.js I included the file and simply told my app to use the globalLocals:

var middleware = require('./config/middleware');
app.use(middleware.globalLocals);

Afterwards without any other changes I integrated this into my ejs template and it worked:

<h1><%= title %></h1>

Great!

After this was done I played a bit with the indexpart of my middleware and also integrated this one via in my app.js but in a different way, because I just want to make this "index" variables available for my index router for a clear seperation!!

app.use("/", middleware.index, indexRouter);

So now I was able to access the values defined in the middleware and use them in ejs. BUT I was no longer be able to access any of my globalLocals and I don´t understand WHY?

Can someone tell me how I can keep the seperation as descibed above and access both objects in my ejs template?

score 1 · Accepted Answer · answered May 15 '19 at 13:40

when you do this

res.locals = {
                // properties
            };

you're overriding previous values of locals from previous middlewares calls (because you're creating a completely new object). You need to extend res.locals with the new values, not create a completely new object. To do so, use Object.assign() which will copy the new values (second parameter) into the object with the old values (first parameter) - keep in mind that if they are named the same, you will be overriding them!

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

index: async function (req, res, next) {
    res.locals = Object.assign(res.locals, {
        index: "index2",
        loggedIn: req.user ? true : false,
        linkObj: await url.getAllUrl()
    });
    next();
}

This totally makes sense, don´t know how i missed that. Thanks a lot, it worked! — el solo lobo, May 15 '19 at 13:47

Creating Middleware Global vs local var

1 Answers1