HTML placeholder屬性用於在表單字段中顯示簡(jiǎn)短提示文本，例如輸入郵箱時(shí)顯示“Enter your email”。 1. 它適用於提供格式示例，如日期格式、用戶(hù)名和電話號(hào)碼。 2. 不應(yīng)替代標(biāo)籤，避免屏幕閱讀器無(wú)法識(shí)別。 3. 避免冗長(zhǎng)說(shuō)明，保持簡(jiǎn)潔。 4. 搭配可見(jiàn)標(biāo)籤使用，確保關(guān)鍵信息不丟失。 5. 注意可訪問(wèn)性，避免顏色對(duì)比度低或依賴(lài)其傳達(dá)必要信息。正確使用placeholder能提升表單易用性。

When you want to give users a quick hint about what they should enter into a form field, the HTML placeholder attribute is a handy tool. It displays a short text inside the input field that disappears when the user starts typing. While it seems simple, there are some important considerations to make sure it's used effectively.

What the placeholder attribute does

The placeholder attribute provides a brief hint or example value for an input field. It's often used in form fields like search bars, email inputs, or name fields. For example:

 <input type="text" placeholder="Enter your email">

When this input appears on the page, the text "Enter your email" will show up inside the box, faded or lighter in appearance than normal text. Once the user clicks into the field and starts typing, the placeholder disappears.

This can be useful for giving quick guidance without needing extra labels or tooltips. However, it's not a replacement for proper labeling — more on that later.

When to use placeholder text

Placeholders work best when they offer a simple example or format suggestion. Here are a few good use cases:

• Showing expected date formats: placeholder="YYYY-MM-DD"
• Giving an example of a username format: placeholder="john_doe123"
• Indicating how to structure a phone number: placeholder="(555) 123-4567"

They're especially helpful when the expected input isn't obvious from the label alone. But again, placeholders shouldn't replace labels entirely. Screen readers may not always read them reliably, which can cause accessibility issues if there's no visible label.

Also, avoid using placeholders as instructions or long explanations. Keep them short and to the point.

Common mistakes with placeholders

A lot of developers fall into a few traps when using placeholders. Here are some common ones:

• ? Using placeholder text instead of a <label>
  This can confuse users who might forget what the field is for once they start typing.

• ? Putting full sentences or instructions in the placeholder
  Something like “Please enter your full name here” is too long and gets cleared as soon as the user types.

• ? Relying on placeholders for critical information
  Since placeholder text disappears when the field has content, it's not a good place to put anything essential.

To avoid these pitfalls, always pair placeholders with a visible label, keep the placeholder text short, and don't treat it as the main explanation of what the field is for.

Accessibility tips for placeholder use

Even though placeholders are visual helpers, they need to support accessibility standards too. Here are a few things to consider:

• Make sure each input has a clear associated label using the <label> tag.
• Avoid styling placeholder text too faintly — it should still be readable for users with visual impairments.
• Don't use placeholders alone to convey required formatting; mention it in the label or nearby text if needed.

For example:

 <label for="phone">Phone Number (format: (555) 123-4567)</label>
<input type="text" id="phone" placeholder="(555) 123-4567">

This way, the format is explained even if the placeholder isn't visible anymore.

Using the placeholder attribute well means balancing helpfulness with clarity and accessibility. It's a small feature, but when used right, it makes forms easier to understand at a glance.

基本上就這些。

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