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How to run middleware on each React page in express server

I'm running an express server and if no other certain URLS aren't met, the user is redirected to the React App:
app.get("*", verify, (req, res) => {
if (maintenance) {
return res.sendFile("./maintenance.html", { root: __dirname });
}
return res.sendFile(
path.resolve(__dirname, "../frontend/build", "index.html")
);
});
This successfully runs the verify middleware needed to check if the user making the request is logged in, if not it redirects them to another service for them to login.
I would've thought that since all URLS that are being used are going through the whole web app is going through this express server, the verify middleware would've been executed no matter what page the user is on. However, this middleware is only executed upon either opening the site on a browser that hasn't been to the site yet (not cached) or if the user force refreshes the page.
I'm new to React and this has led me to believe that React loads the whole app, and upon each change of page (for example from /home to /profile) it doesn't change the url, just loads the portion of the app that's already loaded and so no matter what page the user is on, express will always see that the user is only on the root domain.
How would I get pass this without doing any of this logic on the frontend side. E.g. run the verify function before each page on the react app is loaded into view

Since React is all client side rendering you will need to handle that middleware in your React router, not your Node router. On the frontend we call this "middleware" protected routes.
The overall point is, you will need to protect those routes on the frontend, as when you change a page in React, Node does not know about it (because React is client side rendered).

How does Express and React Routes work on initial GET request from browser?

I'm new to the react world and to the fullstack world as a whole but I've searched endlessly for an answer to the following and some guidance would be really appreciated.
I'm creating an app using React and Express. It requires authentication so I was planning on using Passport to help. The client side JS uses React Routers to navigate through the website. That's all fine but my issue is with the initial GET request made by the browser.
I'll first describe my specific app requirements and then generalize what I don't understand.
As I said, my application requires OAuth2 authentication. If you try to GET a path on my website and you're not logged in, it should just load the login page. If you are logged in, then load as normal and find your path. Similar to facebook, I'd like the login URL to be the same as the "feed" page. So similar to how facebook.com '/' route is either the login page or your new feed depending on whether you are signed in, I want the same thing.
From what I understand, Passport authenticates on the back end by checking the request header. So I understand that I should have some kind of middleware that says "if user is signed in, continue down the routes otherwise render sign in page" ... How is this done? What would the code look like? My only experience with Express was from an intro class which used res.render to send back an HTML file and pass it through some template engine like handlebars. But I have no idea how it'd work with react routes. Would i still use res.render()? Something else?
Let's say my index.html has the root div to inject the react into. If I had to guess, I'd send back that index.html page with the .js file with the routes and somehow on the backend send back the route I want it to match on my react routes (either the login one or the user requested)??
More generally, I guess I'm just confused how the initial request to a website using react routes is done. 1) How does the server interact with everything to render what I asked for? 2) What would the code look like for that. My only experience with React is from a basic Udemy course that just used "react-scripts start" to render the page.
After spending the entire day Googling this question it led me to SSR which is a rabbit-hole of its own and I'm not even sure if its what I need to help me. Is it?
I'm clearly missing some fundamental knowledge as this is really tripping me up so if you have any resources to learn more just post them. Thanks!

I understand your struggle as I've had to go through it myself when combining front-end with back-end, specifically React and Node. So first things first, we know that the browser/client will always initiate a request to the server, so how does React Router take control of the routes? Well its plain simple actually, all you have to do is return the entire react app from any route from your express server. The code will look something like this:
const express = require('express');
const app = express();
app.get('/*', (req, res, next) => {
// Return React App index.html
});
app.listen(3000);
Once the react app renders on the user browser (don't worry about paths, as react will automatically render according to the URL based on the code you wrote in the client side, it will also take care of authentication vs feed page when it will scan for your local storage, cookies, etc), it will take control of routing, instead of a request going to the express server. But what happens when we request data from our server, well it returns react app on each route so we need to setup an api route to handle any data requests.
app.get('/api/v1/*', (req, res, next) {
// Return some data in json format
});
Hopefully, this gives you insight about what you were looking for.

I think the fundamental gap you're struggling with stems from that lot of those 'intro courses' shove the entire browser client into the application server to get things up and running quickly, as in, the Node server renders the entire React app AND operates as an API...
// Ajax request from React app to: http://example.com/api
app.use('/api/*'),()=> {
res.send({ <!-- some JSON object -->})
})
// User visits in browser: http://example.com/**/*
app.use('/*',()=>{
res.render(<!-- entire React App sent to browser -->)
})
The first request (assuming the user doesn't visit /api/* ) will just send down the React bundle. Further user navigation within the client would generally send XHR requests (or open WebSockets) from the React app to Express routes running on the same node program.
In many situations it makes sense to have these parts of your program separated, as by having react delivered from a completely different location than where it requests data. There's many reasons for this, but optimizing computing resources to their differing demands of CPU, memory, network .etc and manageability of code/deployment are the big reasons for me.
For example...
User visits: http://example.com *
Nginx, Apache, a 'cloud proxy' .etc direct the traffic to a static React bundle, which has no authentication and never makes contact with your Node server.
If the user has Authenticate previously they will have token in local storage (if you're using JWTs for Authentication) and your React app will be configured to always check for these tokens when you first it is initially loaded.
If the user has a token it will send an Ajax request in the background with the token as a Header Bearer and will send back user data, then redirect them to an 'Authenticated page' like the FB feed you mention.
If they don't have a token or the token Authentication fails then React will redirect them to the Login or Registration page
React
React basically high jacks the browser's native 'location' functionality (whats displayed after you domain name). So any events after the initial page load (buttons clicks and such) are handled entirely by React internally and uses those routes to determine what to display or what data to fetch from the API through Ajax (XHR).
If the user performs a hard page reload then that request will go back to the server and it will perform the whole cycle over again
React Router
Allows you to do 2 things simultaneously...
Manipulate the browser Location and History objects.
Use that History and Location information elsewhere by detecting changes and sending off events.
SSR
I've only toyed around with SSR so I can speak to it, but its provides extremely low latency for initial renders, doing it in 1 network request, so you want to use it areas of your program where thats important.
Not sure if this answers you question, but let me know if you would like me to elaborate on anything or provide some more detailed resources.

SSR is a little bit confuses for developer that has less experience, let forget it for now.
It will be more easier for you to assume that frontend JavaScript (React) and backend Javascript (NodeJS) are two separate apps, and they communicate to each other via API.
here the code that show Login component and Feed component depending on whether you are signed in
import React, { Component } from "react";
import axios from "axios";
class Home extends Component {
constructor() {
const accessToken = localStorage.getItem("accessToken");
this.state = {
accessToken,
feeds: []
};
}
componentDidMount() {
if (this.state.accessToken) {
axios(`api/feeds?accessToken=${this.state.accessToken}`).then(({ data }) => {
this.setState({
feeds: data
});
});
}
}
render() {
if (this.state.accessToken) {
return <FeedsComponent feeds={this.state.feeds} />;
}
return <LoginComponent />;
}
}
and this is your backend
const express = require("express");
const app = express();
app.get('/api/feeds', (req, res, ) => {
const feeds = [
{},
{}
]
res.status(200).json(feeds);
});
app.listen(3001);
just keep in mind that they are two separate apps, the can be in two different folder, different server, different port.

Simply point Express to the folder containing your React files or build files.
app.use(express.static(__dirname + '/dist'));
where 'dist' contains the build files
See docs for more details

What is relationship between Express routes and client routes in NextJS?

I'm a NextJS newbie and trying to understand the relationship between routes defined in Express and those defined in the 'client', React portion of NextJS. Specifically, if one defines a route on the Express side, such as
router.get("/aLonelyRoute",(req,res)=> {
res.end("You made it!")
})
that doesn't have a corresponding 'page' on the client side (we have the following pages in our React app
pages/index.js
pages/something.js
pages/another.js
), if a request is made to /aLonelyRoute from the browser, will this always be served from the Express server, never rendered from the client?
Also, is it true that if the Express server serves a page that *does *correspond to a route reflected on the 'client' side, then app.render automagically serves it either from the server or renders it from the client, depending:
router.get("/something",(req,res)=> {
app.render(req,res,'something',query)
})
Am I on the right path in understanding this?

You use express for a custom SSR(Server Side Rendering). - In a simple way when you refresh the page or type the URL in url bar and press enter. Express and Next.js router work together to serve the page however it depends on what kind of render has been asked for. if it is a Client side rendering, then next.js will take over and if SSR, then Express will take over first(Next.js will ask for express to take over).
server.get('/p/:id', (req, res) => {
const actualPage = '/post'
const queryParams = { title: req.params.id }
app.render(req, res, actualPage, queryParams)
})
In above example, if there is a client side rendering, user will go something like /post/a-cool-post but server will receive /post?id=a-cool-post which was masked to /p/a-cool-post. Note that /p/... doesn't exists. it is a mask URL. look at as in this example.
<Link as={`/p/${post.id}`} href={`/post?title=${post.title}`}>
<a>{post.title}</a>
</Link>
Long story short, it means we are asking express (in this case server side rendering) if a route is something like /p/a-cool-post, go and give us /post/a-cool-post which is a client side rendering. so the route in client and server will be the same.
First question:
/aLonelyRoute is only in express and there is no code to tell what is it equivalent in client-die. so it will only render from Server.
Second question:
Yes it is correct. Depends what user ask for, if they type url in url bar and press enter
and refresh the page, then express and if you use Next Router for routing, then it will be client side.

NextJS routing: why do there need to be different client and server routes?

I'm somewhat new to React, but wholly new to NextJS, which I'm trying to teach myself. I've been going through the NextJS 'getting started' tutorial, as well as looking at some other tutorials. I don't understand why there is a need to distinguish between client routes and routes on the server, that is, why the client route given as an example uses a query, whereas the server route does not. I know that I am not seeing the forest for the trees, so if anyone can point me in the right direction of 'grokking' NextJS routes, I'd appreciate it.
From this tutorial, on the client side we might have
<Link href={`/blog?slug=${slug}`} as={`/blog/${slug}`} prefetch>
...
</Link>
which requires us (it would seem) to set up an Express server and handle the route
/blog/:slug
OK. But why? Why isn't the local link simply
<Link href={`/blog/${slug}`} prefetch>
...
</Link>
? Or, alternatively, why doesn't NextJS handle server-side the route /blog?slug=${slug} ?
I can follow what the NextJS site 'getting started' tutorial (I input the code myself and test it) is doing, but as far as routing I am a bit lost as to what I'm doing and why. Clearly I am missing a crucial (and elementary) element here, and would appreciate clues as to the error of my ways.

If you look at the route
/blog/${slug}
Here slug can take different values as it a parameter. If you want NextJs to handle such routes you need to implement a route for each value that slug can take. For example.
/blog/slug1
/blog/slug2
/blog/slug3
And this number can grow very quickly. Hence we use an Express server so that we can intercept request to route /blog and pass slug as parameter to the blog page.

You do not need different client and server routes. That is not compulsory unless you are using client-side routing explained here, with dynamic routes.
If you do not want to use that you can switch for server-side routing with our old friend<a> which does not require separate links.
NextJS handles server-side route queries. Below is a simple example for that -
server.get("/dashboard", (req, res) => {
const actualPage = '/dashboard';
const queryParams = {
username: req.query.username
};
app.render(req, res, actualPage, queryParams);
});
In above example, when you open page - /dashboard?username=amit, you can get the value passed in URL query in your page which you can retrieve using - getInitialProps function.
To get data from URL query with server-side routing, you must create your page with getInitialProps function. Example is as below --
Dashboard.getInitialProps = async(ctx) => {
const query = ctx.query;
const username = query.username;
return {"username": username};
}
Above code sends data from url query as page props. Server returns that data to the page in req.
Now you must create _app page with getInitialProps function to make this work.

React with Adonis

I am trying to integrate React with Adonis Js to build an SPA. Adonis handles routing to an SPA by
Route.any('*', function * (request, response) {
yield response.sendView('home')
})
I have done exactly that in app > Http > routes.js
Then I created a home.njk in resources > views to act as the landing page for my application. Now, I have a react file where I have created a footer. I want to handle all the links in the footer with React-router. React router handles urls to navigate to a page. However, the above code(in Adonis) says that any url (*) is going to render 'home'. That is exactly what is happening.
How do get around it? Thanks!

You should define your api routes before the route *.
Adonis Router will go through your routes.js file and get the first route that match.