ESP/frontend/src/settings.js

var myForm = document.getElementById('myForm')
myForm.addEventListener('submit', function(e) {
    e.preventDefault();
    //var data = JSON.stringify(formData(myForm));
    loadJSON(formData(myForm))
})

function formData(form) {
let el = form.querySelectorAll('input[type="text"]');
let ballast = document.getElementById('myBallasts').value;
let myData = '';
    myData += 'ballast' + '=' + ballast + '&';
    for (var x = 0; x < el.length; x++) {
    let name = el[x].name;
    let value = el[x].value;
        //myData[name] = value;
        myData += name + '=' + value + '&'
    }
    return myData.slice(0, -1);
}

function loadJSON(data) {
    const url = '/settings.html';
    console.log(data)
    const myData = data
    fetch(url, {
            method: 'post',
            headers: {
                "Content-type": "application/x-www-form-urlencoded; charset=UTF-8"
            },
            body: myData
        })
        // .then(function (response) {
        // 		return response.json()
        // }).then(function (data) {
        // 		console.log(data)
        // })
        .catch(error => console.log(error))
}