这个 router.get("/".......) 函数是如何工作的？

Question

I'm new to express and ES6 in general. I dont understand the notation of what exactly is going on in the line where we have router.get(. We have 'auth' which is being passed as a parameter but what exactly is happening and how does router.get know how to handle it? At a glance it I've created a file named auth.js which has been imported as auth and that is the object is what we are talking about (please correct me if my terminology is wrong). Or is auth a function and we've passed the function into get and it will run this auth function when router.get is called?

const router = express.Router();
const auth = require("../../middleware/auth");

const User = require("../../models/User");
// @route    GET api/profile
// @desc     Test route
// @access   Public

router.get("/", auth, async (req, res) => {
    try {
        // we are omitting the password
        const user = await User.findById(req.user.id).select("-password");
        res.json(user);
    } catch (err) {
        console.error(err.message);
        res.status(500).send("Server Error");
    }
});

module.exports = router;```

Answer 1

auth is a middleware function that gets to preprocess the request before the handler receives it. the auth function is most likely attaching the user/id to the request, which the handler then uses to query for the actual User object.

Without seeing the auth implementation I can't say exactly what it's doing, (and it's been a while since i've worked in express) but just as an example it could be looking at cookies or request headers to get the user id and attach it to the request object so all subsequent handlers have easy access to it.

If you look at the documentation for router.METHOD you'll see that it takes as many callbacks as you want. Each function can do whatever it needs to do and then call next() to pass processing to the next handler, or it can handle the request itself, responding and/or stopping further processing.

Answer 2

The auth which you have written is a Router-level middleware. It will call before the function execute inside the route.

If your authentication failed then you will get bad response/error response. If your authentication passes then only you will allow to request.

For more info see express official docs https://expressjs.com/en/guide/using-middleware.html#middleware.router

Answer 3

auth 是一个中间件函数，如果您尝试访问的路由没有通过 auth 中间件，您将收到错误消息。

Answer 4

Found out that in the other versions of node, the error of "route.get is not a function" can be resolved by using app.get , app.post or whichever API route you where creating. This resolve needs you to remove the declaration line var router= express.Router() completely and have app = express; //(assuming you assigned imported app=require('express'); app = express; //(assuming you assigned imported app=require('express');