¿Cómo restablecer el estado del botón a deshabilitado después de restablecer el formulario?

//validate form input
function validateForm() {
  let formCheck = document.forms['myForm'].elements;
  let canSubmit = true;

  for (let i = 0; i < formCheck.length; i++) {
    if (formCheck[i].value.length == 0) canSubmit = false;
  } 
  submitThis.disabled = !canSubmit;
}

//prevent form submission, alert if form is submitted, reset form
document.getElementById('submitThis').addEventListener('click', function(e) {
  e.preventDefault();
  alert('Awesomeness! The form will now reset.');
  myForm.reset();
  validateForm();
})

body {
  font-family: sans-serif;
  margin: 0;
  padding: 0;
  height: 100vh;
}

h2 {
  text-align: center;
}

form {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  flex-direction: column;
}

form input {
  margin: 0.5em 0;
  padding: 0.5em;
  border-radius: 5px;
}

form input[type=submit]:active {
  background-color: darkblue;
  color: white;
}

    <form name="myForm" id="myForm" action="/">
      <h3>My Form</h3>
      <input type="text" id="fName" placeholder="First Name" onkeyup="validateForm()" />
      <input type="text" id="address" placeholder="Street Address" onkeyup="validateForm()" />
      <input type="text" id="addCity" placeholder="City" onkeyup="validateForm()" />
      <input type="text" id="addState" placeholder="State" onkeyup="validateForm()" />
      <input type="number" id="addZip" placeholder="Zip Code" onkeyup="validateForm()" />

      <!-- submit form -->
      <input type="submit" id="submitThis" value="Submit" disabled="disabled"/>
    </form>