var form = document.forms[0], // form element to be "readonly"
btn1 = document.querySelectorAll('button')[0],
btn2 = document.querySelectorAll('button')[1]
btn1.addEventListener('click', lockForm)
btn2.addEventListener('click', lockFormByCSS)
function lockForm(){
btn1.classList.toggle('on');
[].slice.call( form.elements ).forEach(function(item){
item.disabled = !item.disabled;
});
}
function lockFormByCSS(){
btn2.classList.toggle('on');
form.classList.toggle('lock');
}
form{ position:relative; }
form.lock::before{
content:'';
position:absolute;
z-index:999;
top:0;
right:0;
bottom:0;
left:0;
}
button.on{ color:red; }
<button type='button'>Lock / Unlock Form</button>
<button type='button'>Lock / Unlock Form (with CSS)</button>
<br><br>
<form>
<fieldset>
<legend>Some Form</legend>
<input placeholder='text input'>
<br><br>
<input type='file'>
<br><br>
<textarea placeholder='textarea'></textarea>
<br><br>
<label><input type='checkbox'>Checkbox</label>
<br><br>
<label><input type='radio' name='r'>option 1</label>
<label><input type='radio' name='r' checked>option 2</label>
<label><input type='radio' name='r'>option 3</label>
<br><br>
<select>
<option>options 1</option>
<option>options 2</option>
<option selected>options 3</option>
</select>
</fieldset>
</form>