要創(chuàng)建HTML下拉菜單中預選的選項，需在目標標籤中添加selected屬性；例如Banana會使“Banana”在頁面加載時默認被選中；1. 只有一個選項應包含selected屬性（除非是多選下拉框）；2. selected是布爾屬性，只需存在即可生效，無需賦值；3. 若無selected屬性，瀏覽器通常默認選擇第一個選項；4. 可結合JavaScript（如設置value值）或服務端語言根據(jù)用戶數(shù)據(jù)動態(tài)預選；5. 該方法簡單、原生支持，適用於靜態(tài)和動態(tài)場景。

To create a pre-selected option in an HTML dropdown menu (ie, a <select></select> element), you use the selected attribute on the <option></option> you want to be selected by default when the page loads.

Use the selected attribute

Inside your <select></select> dropdown, add selected to the <option></option> that should appear as the default choice:

 <select name="fruits">
  <option value="">Choose a fruit</option>
  <option value="apple">Apple</option>
  <option value="banana" selected>Banana</option>
  <option value="orange">Orange</option>
</select>

In this example, "Banana" will be displayed as the selected option when the page first loads.

Key points to remember:

• Only one option should have the selected attribute in a standard dropdown (unless it's a multiple select).
• The selected attribute is boolean — just including it makes the option selected. You don't need to set it to "true" ; selected or selected="selected" both work.
• If no option has selected , the browser will typically pick the first option by default.

Pre-selecting based on user data or preferences

In real applications, you might want to pre-select an option based on saved user preferences, form data, or dynamic content. This can be done using server-side languages (like PHP, Python, etc.) or JavaScript.

For example, with JavaScript:

 <select name="color" id="colorSelect">
  <option value="red">Red</option>
  <option value="green">Green</option>
  <option value="blue">Blue</option>
</select>

<script>
  // Set "Green" as selected after page loads
  document.getElementById("colorSelect").value = "green";
</script>

This is useful when loading saved settings or reacting to user actions.

Summary

• Use selected in the <option></option> tag to set a default.
• Works right in plain HTML.
• Can be combined with JavaScript for dynamic selection.

Basically, just add selected to your preferred <option></option> — it's simple and widely supported.

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