Выборка элементов формы

<input type="text">

const a = element.value;
element.value = 'new value';

<input type="checkbox">

const a = element.checked; 
element.checked = true;

<input type="radio">

<input type="radio" name="radio" value="r1">
<input type="radio" name="radio" value="r2">
<input type="radio" name="radio" value="r3">

const radio = document.querySelectorAll('input[type="radio"]');

for(let i=0; i<=radio.length-1; i++) {
	if(radio[i].checked) {
		let value = radio[i].getAttribute('value');
		console.log(value);
	}
}

radio.disabled = true;   

<select>

const select = document.querySelector('select');
const a = select.value;
const a = select.options[select.selectedIndex].value;
const a = select.options[select.selectedIndex].text;