javascript Hide/show div on checkbox: checked/unchecked

Question

I am trying to make a function in javascript, that will hide / show particular div in my registration form, depending on the state of my checkbox (checked or not). Here is

Answer 1

You could use

var elem = document.getElementById('powermail_fieldwrap_331');
document.getElementById('powermail_field_doruovaciaadresa2_1').onchange = function() {
    elem.style.display = this.checked ? 'block' : 'none';
};

Demo

---

If you want to hide it by default, you could use #powermail_fieldwrap_331{display:none;}. But if you want to be sure, better use

var elem = document.getElementById('powermail_fieldwrap_331'),
    checkBox = document.getElementById('powermail_field_doruovaciaadresa2_1');
checkBox.checked = false;
checkBox.onchange = function doruc() {
    elem.style.display = this.checked ? 'block' : 'none';
};
checkBox.onchange();

Demo