同样，这对我来说也很有效:

<textarea class="form-control" rows="3" name="msg" placeholder="Your message here." onfocus='this.select()'>
<?php if (isset($_POST['encode'])) { echo htmlspecialchars($_POST['msg']);} ?>
</textarea>

在这种情况下，$_POST['encode']来自:

<input class="input_bottom btn btn-default" type="submit" name="encode" value="Encode">

PHP代码被插入到和标记之间。

几点注意事项和澄清:

placeholder='' inserts your text, but it is greyed out (in a tool-tip style format) and the moment the field is clicked, your text is replaced by an empty text field. value='' is not a <textarea> attribute, and only works for <input> tags, ie, <input type='text'>, etc. I don't know why the creators of HTML5 decided not to incorporate that, but that's the way it is for now. The best method for inserting text into <textarea> elements has been outlined correctly here as: <textarea> Desired text to be inserted into the field upon page load </textarea> When the user clicks the field, they can edit the text and it remains in the field (unlike placeholder=''). Note: If you insert text between the <textarea> and </textarea> tags, you cannot use placeholder='' as it will be overwritten by your inserted text.

下面是我的jsFiddle示例。这很好:

<textarea name='awesome'>Default value</textarea>

你可以使用this.innerHTML。

<textarea name="message" rows =" 10" cols =" 100" onfocus="this。innerHTML= " ">在这里输入您的消息…textarea > < /

当文本区域被聚焦时，它基本上会使文本区域的innerHTML成为空字符串。

你可以使用占位符属性，它不添加默认值，但可能是你正在寻找的:

<textarea placeholder="this text will show in the textarea"></textarea>

点击这里查看- http://jsfiddle.net/8DzCE/949/

重要提示(Jon Brave在评论中建议):

占位符属性不设置文本区域的值。相反，“占位符属性代表了一个简短的提示(一个单词或短语)，旨在帮助用户在控件没有值时输入数据”[并且一旦用户单击进入文本区域，它就会消失]。它永远不会作为控件的“默认值”。如果你想这样做，你必须把想要的文本放在这里是实际的默认值，就像这里的其他答案一样

你也可以添加"value"属性并设置如下:

<textarea value="your value"> </textarea>