HTML required属性用法及代码示例

它是一个布尔属性，用于指定在提交表单之前必须填写输入元素。

元素：此属性可以与以下列出的三个元素相关联：

<输入>
<选择>
<textarea>

<输入>：

用法：
```
<input required>
```

示例1：

<!DOCTYPE html> 
<html> 
    <head> 
        <title>required Attribute</title> 
        <style> 
            h1, h2 { 
                color:green; 
                font-style:italic; 
            } 
            body { 
                text-align:center; 
            } 
        </style> 
    </head> 
    <body> 
        <h1>GeeksForGeeks</h1> 
        <h2>required attribute in input Field</h2> 
        <form action=""> 
            Username:  
            <input type="text" name="usrname" required> 
            <br> 
            Password:
            <input type="password"name="password"> 
            <br> 
            <input type="submit"> 
        </form> 
    </body> 
</html>

Output:

<select>：此元素还可以使用必需的属性。

用法：
```
<select required>
```

示例-2：

<!DOCTYPE html> 
<html> 
    <head> 
        <title>required Attribute</title> 
        <style> 
            h1, h2 { 
                color:green; 
                font-style:italic; 
            } 
            body { 
                text-align:center; 
            } 
        </style> 
    </head> 
    <body> 
        <h1>GeeksForGeeks</h1> 
        <h2>required attribute in select Field</h2> 
        <form action=""> 
            <select required> 
                <option value="">None</option> 
                <option value="ds">Data Structure</option> 
                <option value="algo">Algorithm</option> 
                <option value="os">Operating System</option> 
                <option value="cn">Computer Network</option> 
            </select> 
            <input type="submit"> 
        </form> 
    </body> 
</html>

Output:

<textarea>：此元素也可以使用必需的属性。

用法：
```
<textarea required>
```

示例3：

<!DOCTYPE html> 
<html> 
    <head> 
        <title>required Attribute</title> 
        <style> 
            h1, h2 { 
                color:green; 
                font-style:italic; 
            } 
            body { 
                text-align:center; 
            } 
        </style> 
    </head> 
    <body> 
        <h1>GeeksForGeeks</h1> 
        <h2>required attribute in Textarea Field</h2> 
        <form action=""> 
            <textarea rows="7" cols="50" 
                             name="comment" required> 
            </textarea> 
            <input type="submit"> 
        </form> 
    </body> 
</html>

Output:

支持的浏览器：必需属性支持的浏览器如下：

谷歌浏览器5.0+
Internet Explorer 11.0以上
Firefox 4+
Opera 9.7+

相关用法

注：本文由纯净天空筛选整理自ManasChhabra2大神的英文原创作品 HTML | required Attribute。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。