How to fix Node express error: cannot GET - node.js

Question

I'm trying to create a simple backend api for an app I'm working on (create-react-app) and decided to use node express. I'm getting the error 'cannot GET' when I open my browser and I don't understand why.
Here is my server/index.js file:
const express = require("express");
const PORT = process.env.PORT || 3001;
const app = express();
app.get("/api", (req, res) => {
res.json({ message: "Hello from server!" });
});
app.listen(PORT, () => {
console.log(`Server listening on ${PORT}`);
});
app.listen(PORT, () => {
console.log(`Server listening on ${PORT}`);
});
Here is my start script:
"scripts": {
"start": "node index.js"
}
In my console I see this error:
Failed to load resource: the server responded with a status of 404 (Not Found)
This is my folder structure:
I have an app called 1REPMAX that contains the folders
>build
>node-modules
>public
>server
>node_modules
>index.js
>package-lock.json
>package.json
>src
.gitignore
package-locj.json
package.json
So what I've been doing is I cd into server and then run npm start.
When I open my browser to localhost:3001 I get the error. Any help on what I'm doing wrong? If more information is needed just let me know. Also, when I ran npm start the first time it started up fine, but now every time I run it I get this error:
code: 'EADDRINUSE',
errno: -48,
syscall: 'listen',
address: '::',
port: 3001
I don't know if this has something to do with it or not.

Answer 1

The first error is caused because your app is not listening to the / path, only the /api path.
The second error is caused by a duplicate app.listen() call in your server/index.js file.
Your code should look something like this in order to resolve the issues:
const express = require("express");
const PORT = process.env.PORT || 3001;
const app = express();
app.get("/", (req, res) => res.send("Main page"));
app.get("/api", (req, res) => {
res.json({ message: "Hello from server!" });
});
app.listen(PORT, () => {
console.log(`Server listening on ${PORT}`);
});