我不知道這段程式碼做錯了什麼，我上網查了一下，我所看到的就是將 window.onload = function() 放在程式碼的開頭。但是，該值始終列印為 null，我無法理解為什麼要這樣做。
這是程式碼：
window.onload = function () {
// Get the select element by its id
const select = document.getElementById("select-filter");
// Get the selected option element
const selectedOption = select.options[select.selectedIndex];
// Get the data-select value
const dataSelect = selectedOption.getAttribute("data-sel");
// Print the data-select value to the console
console.log(dataSelect);
}
<div class="filter-select-container">
<!-- filter selector -->
<div class="filter-selection-container">
<select name="select-filter" id="select-filter">
<option value="filter-all">All</option>
<option value="filter-commercials" data-sel="1">Commercials</option>
<option value="filter-fiction" data-sel="2">Fiction</option>
<option value="filter-music-videos" data-sel="3">Music Videos</option>
</select>
</div>
</div>
感謝您的幫忙:)
您可能意味著
select有一個change偵聽器 ，然後在嘗試記錄之前檢查資料屬性是否已定義。const select = document.getElementById("select-filter"); select.addEventListener('change', handleChange); function handleChange() { const selectedOption = select.options[select.selectedIndex]; const dataSelect = selectedOption.getAttribute("data-sel"); if (dataSelect) console.log(dataSelect); }