SomethingThatDoesntSuck/Src/assets/js/changetheme.js

var elForm,elSelectedTheme1,elSelectedTheme2,currentTheme
mainbody = document.getElementById('mainbody');
currentTheme = document.getElementById('mainbody').getAttribute('class');
elForm = document.getElementById('form-theme');
elSelectedTheme1 = document.getElementById('exampleRadios1');
elSelectedTheme2 = document.getElementById('exampleRadios2');
console.log(elForm,elSelectedTheme1,elSelectedTheme2,currentTheme);

// document.querySelector('input[name="Theme"]:checked').value;

function selectTheme(e){
    if(!elSelectedTheme1.checked && !elSelectedTheme2.checked){
        // elSelectThemeHint.textContent = 'Devi selezionare almeno un tema!'
        console.log('Devi selezionare almeno un tema!');
    }else if (!elSelectedTheme2.checked){
        var selectedTheme = elSelectedTheme1.value;
        mainbody.className = selectedTheme;
    }else{
        var selectedTheme = elSelectedTheme2.value;
        mainbody.className = selectedTheme;
    }
}

elForm.addEventListener('change',function(e){
    selectTheme(e)},
    false);