domejercicio2.html

<!DOCTYPE html>

<html lang="en">
<head>

</head>

<body>
    <fieldset>
        <legend>Billing Information</legend>
        <p>
            <label>
                Postal Address:<br>
                <input name="postaladdress" id="postaladdress"></input>
            </label>
        </p>
        <p>
                Home Address:<br>
            <label>
                <input type="checkbox" name="homepostalcheck" id="homepostalcheck">
                Same as above
            </label>
                <br>
                <input name="homeaddress" id="homeaddress"></input>
        </p>
    </fieldset>


</body>

<script>

    function setHomeAdress(){

        var campo1 = document.getElementById('postaladdress');

        cb=document.getElementById('homepostalcheck')

        document.getElementById('postaladdress').addEventListener('change', () => {         
                    alert(campo1.value);      
            }
          );

           
            document.getElementById('homepostalcheck').addEventListener('click', () => {

            if (cb.checked==true) {      
       
               document.getElementById("homeaddress").disabled = true;

            } else {
                
               document.getElementById("homeaddress").disabled = false;

            }
            });


        }

        setHomeAdress();

</script>


</html>