mayanhavoc/middleware_intro

Middleware

Intro to building middleware for ExpressJS.

app.use will run for every single req (wether it's a GET, POST , etc). If it returns, nothing will run after it, so it's important that if we want our program to keep running, to put a next() at the end so it know to move on to the next middleware.

This can be useful, for example, when you want to use middleware for a group of internal routes or authenticated routes. It's also useful to create 404 pages.

Using middleware to protect routes

Because middleware executes for every single req, we can use it to protect routes. Basically creating functions that check for certain parameters in order to grant access to that route (by allowing the next() command to run if checks pass).

IMPORTANT - This is NOT how you do proper authentication, this is just an example of using middleware to protect routes. In other words, NEVER send a password as a query string.

Example - This protects every single route

app.use((req, res, next) => {
    const { password } = req.query;
    if(password === 'chickennugget'){
        next();
    }
    res.send('Sorry, you need a password')
})

Protecting specific routes

Instead of passing the authentication middleware through app.use as in the previous example, we can actually pass it to the req. When we define a path, i.e. app.get , we pass in a path and we can optionally pass multiple callback functions. These callback functions will behave just like middleware.

const verifyPassword = (req, res, next) => {
    const { password } = req.query;
    if(password === 'chickennugget'){
        next();
    }
    res.send('Sorry, you need a password')
}

app.get('/secret', verifyPassword, (req, res) => {
    res.send('My secret is: Sometimes I wear headphones in public')
})