CustomStateSet.add()

The add method of the CustomStateSet interface adds an item to the CustomStateSet, after checking that the value is in the correct format.

value

A DOMString which must be a <dashed-ident>, with the form --mystate.

Undefined.

DOMException SyntaxError

Thrown if the string is not a <dashed-ident>.

The following function adds the state --checked to a CustomStateSet.

set checked(flag) {
  if (flag) {
    this._internals.states.add('--checked');
}