[checkbox/switch] unchecked value behaviour

Discussion Summary

Currently checkboxes (and switches) have an odd behaviour around their value property and the forms submission behaviour.

Take <input type="checkbox" name="a"> this element will reflect .value as "on", but when a parent form is submitted it won't include any entry for "a".

As the checkbox is unchecked it's quite common to want false submitted when unchecked and true when checked. You can do the latter part by adding value="true" but when unchecked it still won't be included in the form submission (and .value will still return "true".)

There's workarounds using JS where you can listen for the formdata event and manually add the entry when unchecked, but it would be nice if we had a HTML solution to this.

Possibly a new attribute (name tbd) such as uncheckedvalue="false" which includes the input in the form submission automatically and perhaps updates the value getter to return the uncheckedvalue attribute's value when unchecked.

Original comment

I would really like it that when a checkbox is unchecked its value is an empty string.

I don't know about others, but i have to do this hack all the time:

let value = el.value; // other input
if (el.type==='checkbox') { // checkboxes
    value = el.checked ? el.value : '';
}

Start by reproducing the unchecked and checked behavior, including its .value and parent form submission, and review the formdata event workaround described in the issue. Done means an agreed HTML behavior and attribute design that specifies unchecked values, checked values, the value getter, and form submission semantics.