实例演示classList对象和blur事件

<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>实例演示classList对象和blur事件</title>
  </head>
  <style>
    .bgc {
      background-color: blue;
    }
    .bgc2 {
      background-color: yellow;
    }
    .active {
      color: red;
    }
    .boder {
      border: 1px solid black;
    }
    .title {
      font-size: 60px;
    }
  </style>
  <body>
    <h2 class="title">Hello World</h2>
    <script>
      const h2 = document.querySelector('.title');
      // 添加
      h2.classList.add('active');
      h2.classList.add('bgc');
      // 判断
      console.log(h2.classList.contains('hello') ? 'hello world' : 'hello php');
      // 移除
      h2.classList.remove('bgc');
      // 替换
      h2.classList.replace('active', 'bgc2');
      // 动态切换
      h2.classList.toggle('boder');
    </script>
    <!-- 表单非空验证 -->
    <form action="" method="post" id="login">
      <label for="email">邮箱:</label>
      <input type="email" id="email" name="email" value="" autofocus />
      <label for="password">密码:</label>
      <input type="password" id="password" name="password" />
      <!-- 1. type="button" 来表示这是一个普通按钮,没有提交行为 -->
      <button type="button" name="submit" onclick="check(this)">登录</button>
    </form>
    <!-- 表单非空验证 -->
    <script>
      //点击button触发check函数进行验证
      function check(ele) {
        // 禁用默认行为
        event.preventDefault();
        // 防止冒泡
        event.stopPropagation();
        // 非空验证
        // 每一个表单控件input,都有一个form属性,指向所属的表单元素
        // 通过form属性可以获取到表单中所有元素的值
        let email = ele.form.email;
        let password = ele.form.password;
        if (email.value.length === 0) {
          email.setAttribute('placeholder', '邮箱不能为空，请输入');
          email.focus();
          return false;
        } else if (password.value.length === 0) {
          password.setAttribute('placeholder', '密码不能为空，请输入');
          password.focus();
          return false;
        }
      }
      // 失去焦点验证;
      document.forms.login.email.onblur = function () {
        if (this.value.length === 0) {
          this.setAttribute('placeholder', '不能为空，请输入');
          return false;
        }
      };
    </script>
  </body>
</html>
实例演示classList对象和blur事件

实例演示classList对象和blur事件

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