Importing .js or .mjs files using Node webserver

Question

I installed Node.js and wanted to run a webserver that would show an html+javascript page that imports javascript functions from other .js files. Installing Node.js, running the webserver, and hosting a file locally all went very smoothly. But I keep having issues accessing the other .js files that I would like to import from test_functions.html. I have been following various online tutorials, and looking around on stack overflow, trying it in several different ways, but can't get it to work. I am thinking I might need to adjust something in the server.js file to allow my browser to acces the other files I want to import? Using .mjs extensions (instead of .js) I got my browser to recognise the functions I want to import, but it still doesn't manage to import the functions that I define in these .mjs files.

Here is the code for server.js

// use the http library to start the node server
const { read } = require('fs')
const http = require('http')
// additional library for file handling
const fs = require('fs')
// port we want to use
const port = 3000
// filename of the html page we want to show when accessing the server
const file_name = 'test_functions.html'
// create the server

const server = http.createServer(function(req, res){
    // tell the brower we will be writing HTML
    res.writeHead(200, {'Content-Type':'text/html'})
    fs.readFile(file_name, function(error, data){
        if(error){
            res.writeHead(404)
            read.write('Error: File ' + file_name + ' not found')
        } else{
            res.write(data)
        }
        res.end()
    })
})
server.listen(port, function(error){
    if (error){
        console.log('Something went wrong', error)
    }
    else {
        console.log('Server is istenng on port ' + port)
    }
})

My main page, test_functions.html looks as follows

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <script src="test.mjs" type="module">
        </script>
    </head>
    <body>
        <p>Hey, click on the button below to invoke the function</p>
        <input type = "button" onclick = "showAlert()" value = "Click Me">
    </body>
</html>

while the function that I placed in test.mjs looks as follows

export default function showAlert()
{
    alert("welcome");  
} 
console.log('hello')

After trying it in various ways, the browser keeps giving me the following two errors:

Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/html". Strict MIME type checking is enforced for module scripts per HTML spec.
Uncaught ReferenceError: showAlert is not defined at HTMLInputElement.onclick

Does this answer your question? Basic static file server in NodeJS — jsejcksn
– jsejcksn, Commented Jul 30, 2022 at 12:20
Thank you very much! I managed to get it working by expanding the server.js script to search through a public folder where it will source all requested files from. I'll update the question later when I understand a bit better what I did, but basically followed the code from the following video youtube.com/watch?v=gvbVjJnv-b8 — Jeroen
– Jeroen, Commented Jul 30, 2022 at 20:45

Jeroen · Accepted Answer · 2022-08-13 16:14:44Z

To allow the Node server to search through a public folder for all files that are requested by the browser I followed the following tutorial: https://youtube.com/watch?v=gvbVjJnv-b8

I got it all to work in the end by updating the server.js file as follows:

// use the http library to start the node server
const { read } = require('fs')
const http = require('http')

// additional libraries for file handling
const url = require("url");
const fs = require('fs')
const lookup = require("mime-types").lookup;

// server settings
const PORT = 3000
const DEFAULT_PAGE = index.html

// create the server
const server = http.createServer((req, res) => {
    // handle the request and send back a static file from a local folder called 'public'
    let parsedURL = url.parse(req.url, true);
    // remove the leading and trailing slashes
    let path = parsedURL.path.replace(/^\/+|\/+$/g, '');
    if (path == ""){
        path = DEFAULT_PAGE;
    }
    console.log(`Requested path ${path} `);

    let file = __dirname + "/public/" + path;
    // async read file function uses callback
    fs.readFile(file, function(err, content){
        if(err){
            console.log(`File Not Found ${file}`);
            res.writeHead(404);
            res.end();
        } else {
            //specify the content type in the response
            console.log(`Returning ${path}`);
            res.setHeader("X-Content-Type-Options", "nosniff");
            let mime = lookup(path);
            res.writeHead(200, { "Content-type": mime });
            res.end(content);
        }
    });

})
server.listen(PORT, function(error){
    if (error){
        console.log('Something went wrong', error)
    }
    else {
        console.log('Server is istenng on port ' + PORT)
    }
})

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