What happens when we submit a form in HTML if action attribute is empty or contains a url

fetch("https://localhost:8080", obj)
.then()
.catch()

fetch("https://localhost:8080", obj)
.then()
.catch()

const express = require('express');
const path = require('path');

const app = express();
const port = 3000;

app.use(express.urlencoded({extended: false}));
app.use(express.static(path.join(__dirname,'public')));

app.post('/api', (req, res) => {
  console.log(req);
})

app.use('/',(req,res,next) => {
  res.sendFile(path.join(__dirname,'public','index.html'));
});


app.listen(port, () => console.log(`App is listening on port ${port}!`))

const express = require('express');
const path = require('path');

const app = express();
const port = 3000;

app.use(express.urlencoded({extended: false}));
app.use(express.static(path.join(__dirname,'public')));

app.post('/api', (req, res) => {
  console.log(req);
})

app.use('/',(req,res,next) => {
  res.sendFile(path.join(__dirname,'public','index.html'));
});


app.listen(port, () => console.log(`App is listening on port ${port}!`))

<form id="coolform">
  <input />
</form>

<form id="coolform">
  <input />
</form>

document.querySelector('#coolform').addEventListener('submit', (event) => {
  event.preventDefault();//prevent the regular submission from going through

  const formData = new FormData(event.target);
  //process the data here, validate, check, enrich, or just repackage as required by your backend
  fetch('https://localhost:port/api', { options_here })
    .then((res) => {
      //process results
    });
});

document.querySelector('#coolform').addEventListener('submit', (event) => {
  event.preventDefault();//prevent the regular submission from going through

  const formData = new FormData(event.target);
  //process the data here, validate, check, enrich, or just repackage as required by your backend
  fetch('https://localhost:port/api', { options_here })
    .then((res) => {
      //process results
    });
});

document.querySelector('#login').addEventListener('submit', (event) => {
    event.preventDefault(); // Prevent default form submission

    const formData = new FormData(event.target);

    fetch('http://127.0.0.1:5500/Server/public/HTML/form.html', {
        method: 'POST', // Specify the HTTP method
        body: formData, // Send the FormData object
    })
        .then((response) => {
            if (!response.ok) {
                throw new Error('Network response was not ok ' + response.statusText);
            }
            return response.json(); // Parse JSON response if applicable
        })
        .then((data) => {
            console.log('Success:', data); // Handle success
        })
        .catch((error) => {
            console.error('Error:', error); // Handle errors
        });
});

document.querySelector('#login').addEventListener('submit', (event) => {
    event.preventDefault(); // Prevent default form submission

    const formData = new FormData(event.target);

    fetch('http://127.0.0.1:5500/Server/public/HTML/form.html', {
        method: 'POST', // Specify the HTTP method
        body: formData, // Send the FormData object
    })
        .then((response) => {
            if (!response.ok) {
                throw new Error('Network response was not ok ' + response.statusText);
            }
            return response.json(); // Parse JSON response if applicable
        })
        .then((data) => {
            console.log('Success:', data); // Handle success
        })
        .catch((error) => {
            console.error('Error:', error); // Handle errors
        });
});

import express from 'express';
import path from 'path';
import { fileURLToPath } from 'url';
import {router} from '../routes/root.js'
import cors from 'cors';



const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const port = 8080;
const app = express();

//CORS - Cross Origin Resource sharing
const allowedOrigins = ['http://127.0.0.1:5500', 'http://localhost:8080'];
const corsOptions = {
    origin: allowedOrigins,
    optionsSuccessStatus: 200,
  };
 
app.use(cors(corsOptions));

// Serve static file
app.use('/M00967932', express.static(path.join(__dirname, '../public')));

// Handle form submission
app.use(express.urlencoded({extended : false}));


//JSON parser
app.use(express.json());


app.use('/M00967932', router);

app.listen(port, () => {
    console.log(`Server started on port ${port}`);
})

import express from 'express';
import path from 'path';
import { fileURLToPath } from 'url';
import {router} from '../routes/root.js'
import cors from 'cors';



const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const port = 8080;
const app = express();

//CORS - Cross Origin Resource sharing
const allowedOrigins = ['http://127.0.0.1:5500', 'http://localhost:8080'];
const corsOptions = {
    origin: allowedOrigins,
    optionsSuccessStatus: 200,
  };
 
app.use(cors(corsOptions));

// Serve static file
app.use('/M00967932', express.static(path.join(__dirname, '../public')));

// Handle form submission
app.use(express.urlencoded({extended : false}));


//JSON parser
app.use(express.json());


app.use('/M00967932', router);

app.listen(port, () => {
    console.log(`Server started on port ${port}`);
})