HTMLInputElement: checked property

The checked property of the HTMLInputElement interface specifies the current checkedness of the element; that is, whether the form control is checked or not.

The boolean checked property is relevant to the radio (<input type="radio">) and checkbox (<input type="checkbox">) input types.

The presence of the HTML checked attribute indicates the checkbox is checked by default. It does not indicate whether this checkbox is currently checked: if the checkbox's state is changed, this content attribute does not reflect the change; only the HTMLInputElement's checked IDL property is updated. The checked attribute is reflected by the defaultChecked property.

When a radio input checked property is true, all other radio inputs with the same name are false. If any radio button in a same-named group of radio buttons is required, as long as one button in the group is checked, the ValidityState object's read-only valueMissing property for each radio button in the group will be false.

A checkbox's value is only included in the submitted data upon form submission if checked is true. The value of the HTMLInputElement.indeterminate property has no effect on a checkbox's checked value.

const inputElement = document.getElementById("contactMail");
console.log(inputElement.checked);
inputElement.checked = true;