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In Express, I'm using different routers for each of my routes, like this:

const express = require('express');
const postRouter = require('./postRouter');
const userRouter = require('./userRouter');
const app = express();


app.use('/posts', postRouter);
app.use('/users', userRouter);

And then in my router files, I have the routes.

However, let's say that on all my pages I'm using sessions. If I want to do this, I have to say router.use(sessionMiddleware); in each router file.

My question is is that if I can still use multiple routers without having to specify the middleware in each file. I've tried app.use(); but that doesn't work.

Thank you

Tejas_hooray
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1 Answers1

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You need to do what you claim doesn't work:

app.use(sessionMiddleware);

However I can guess why your attempt doesn't work. It probably comes from your misunderstanding of how Express work.

At it's core express is a middleware processing engine. You configure a list of middlewares in Express (endpoints are also middlewares, they just happen to be the last to be executed) and Express will process them one at a time in order.

The last sentence is the most important to understand: Express will process middlewares one at a time in order.

So if you do something like

app.use('/posts', postRouter);
app.use('/users', userRouter);
app.use(sessionMiddleware);

What you are doing is tell express to:

  • First see if the request matches '/posts', if it does execute postRouter
    • If postRouter is executed see if the route call the next() function without any argument. If next() is called continue processing.
    • If next() is called with any argument stop processing and proceed to the error handler (by default this will send an error page back to the browser)
    • If next() is not called stop processing
  • If processing continues, second see if the request matches '/users' if it does execute userRouter
    • If userRouter is executed see if the route call the next() function without any argument. If next() is called continue processing.
    • If next() is called with any argument stop processing and proceed to the error handler
    • If next() is not called stop processing
  • If processing continues execute sessionMiddleware

So if your flow (yes, it's a program flow, not simply API calls to Express) is like the above this means the sessionMiddleware will not get executed for the /posts and /users routes.

This means you need to change your program flow as follows:

app.use(sessionMiddleware);
app.use('/posts', postRouter);
app.use('/users', userRouter);

As you can see, Express is very flexible. Say for example you want /posts to use your session middleware but not /users. You can do this instead:

app.use('/users', userRouter);
app.use(sessionMiddleware);
app.use('/posts', postRouter);
slebetman
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