在选择相关的下拉选项之前，如何在页面加载时默认隐藏文本字段？

<select id="dropdown">
  <option value="option1">Option 1</option>
  <option value="option2">Option 2</option>
  <option value="option3">Option 3</option>
</select>

<input type="text" id="textfield" style="display: none;">

window.onload = function() {
  var dropdown = document.getElementById("dropdown");
  var textfield = document.getElementById("textfield");

  dropdown.addEventListener("change", function() {
    if (dropdown.value !== "") {
      textfield.style.display = "block";
    } else {
      textfield.style.display = "none";
    }
  });
};