data: {
    insereDados : "true",
    inputDado : arr
}

<form action="#">
  <input type="checkbox" name="data[]" value="1"> 1
  <input type="checkbox" name="data[]" value="2"> 2
  <input type="checkbox" name="data[]" value="3"> 3
  <input type="checkbox" name="data[]" value="4"> 4
  <button>Enviar</button>
</form>

const form = document.querySelector('form');
const button = document.querySelector('button');

button.addEventListener('click', function (event) {
  let data = new FormData(form);

  console.log(data.getAll('data[]'));
});