要使輸入字段只讀，需使用readonly屬性。1. 在input標簽中添加readonly屬性即可實現(xiàn)只讀效果；2. readonly允許用戶選擇和復制內(nèi)容，并隨表單提交；3. 與disabled不同，后者不隨表單提交且無法獲得焦點；4. 可通過JavaScript動態(tài)控制只讀狀態(tài)，如設(shè)置input.readOnly = true或false；5. 使用時注意測試表單提交行為、可訪問性及視覺樣式以提升用戶體驗。

You can make an input field read-only by adding the readonly attribute to the <input> tag. This prevents users from modifying the value while still allowing them to select and copy it.

Basic usage of the readonly attribute

The readonly attribute is a boolean attribute, which means you don’t need to assign a value to it. Just include it in the input element like this:

<input type="text" value="This is read-only" readonly>

When this is rendered in a browser, the input will look normal, but users won't be able to edit its content. However, they can still highlight and copy the text, and the value will be submitted with the form if applicable.

Here’s what you should keep in mind:

• The input's value must be set using the value attribute for readonly to have any visible effect.
• You can apply readonly to various input types, such as text, number, email, etc.

How readonly differs from disabled

Both readonly and disabled prevent users from editing an input, but there are important differences:

• readonly inputs submit their values with the form, while disabled inputs do not.
• readonly fields can still receive focus (depending on browser behavior), but disabled fields cannot.
• Styling: Browsers often apply default styles to disabled elements (like grayed-out text), but not always for readonly.

If you're building a form and need to display data that shouldn’t be changed but still needs to be included when the form is submitted, use readonly. If you want to temporarily block interaction and also exclude the value from submission, go with disabled.

When to use JavaScript to toggle readonly

Sometimes you’ll want to control whether an input is read-only based on user actions or other logic. In those cases, you can use JavaScript to dynamically add or remove the readonly attribute.

For example, you might have a checkbox that toggles edit mode:

<input type="checkbox" id="toggleEdit"> Allow editing
<br>
<input type="text" id="myInput" value="Initial value" readonly>

<script>
  const checkbox = document.getElementById('toggleEdit');
  const input = document.getElementById('myInput');

  checkbox.addEventListener('change', function() {
    input.readOnly = !this.checked;
  });
</script>

A few tips when working with JavaScript:

• Use input.readOnly = true to set it read-only, and input.readOnly = false to make it editable again.
• Avoid using removeAttribute('readonly') unless necessary — setting it to false is usually cleaner.
• Be careful mixing readonly and disabled via JS; stick to one unless you have a specific reason.

Final notes

Using readonly is straightforward and effective when you need to show information in a form without letting users change it. It’s especially useful for displaying calculated values, pre-filled data, or confirmation steps.

Just remember:

• Always test how your form behaves on submission.
• Consider accessibility — screen readers may announce read-only fields differently.
• Think about styling: some browsers don’t visually distinguish readonly fields, so adding a custom class might help users understand the input isn’t editable.

基本上就這些。

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