let allInputBoxes = document.querySelectorAll("input[type='checkbox']");
let limit = 2;

function checkboxesChecked() {
  let checkedInputBoxes = document.querySelectorAll(
    "input[type='checkbox']:checked"
  );

  if (checkedInputBoxes.length > limit) {
    this.checked = false;
  }
}

for (const checkbox of allInputBoxes) {
  checkbox.addEventListener("click", checkboxesChecked, false);
}