Javascript 活动无效

Question

我正在尝试 onfocus 和 onblur 事件。它不工作。当我单击电子邮件字段时，该值不会消失。这是我的代码。有什么不对的地方请告诉我。

    <!DOCTYPE html>
    <html>
    <head>
     <title>More Events</title>
    </head>
    <body>
     <form>
      <input type="text" value="your email" name="email" id="email" />
     </form>
    
     <script>
      var emailField = document.getElementById('email');
       emailField.onfocus = function(c) {
        if (emailField.value == 'your email')
         {
          emailField.value == '';
         }
        }
       emailField.onblur = function(c) {
        if (emailField.value == '')
         {
          emailField.value == 'your email';
         }
        
       }
     </script>
    
    </body>
    </html>

Answer 1

赋值运算符错误，变化

emailField.value == '';
...
emailField.value == 'your email';

至

emailField.value = '';
...
emailField.value = 'your email';

Answer 2

您正在使用双等号来赋值：

emailField.value == '';

应该是

emailField.value = '';

在其他方面也是如此。

Answer 3

您在此处使用比较运算符 (==) 而不是赋值运算符 (=):

emailField.value == '';

改为

emailField.value = '';

在代码中：

var emailField = document.getElementById('email');
         emailField.onfocus = function(c) {
            if (emailField.value == 'your email')
                {
                    emailField.value = '';
                }
            }
         emailField.onblur = function(c) {
            if (emailField.value == '')
                {
                    emailField.value = 'your email';//Also here
                }

         }

Answer 4

<form>
    <input type="text" value="your email" name="email" id="email" onfocus="function(this)" />
</form>

<script>
    var emailField = document.getElementById('email');
     emailField.onfocus = function(c) {
        if (emailField.value == 'your email')
            {
                emailField.value = ''; // Here was the problem use assignment operator(=) here emailField.value == '';
            }
        }
     emailField.onblur = function(c) {
        if (emailField.value == '')
            {
                emailField.value = 'your email'; // Here was the problem use assignment operator(=) here emailField.value == '';
            }

     }
</script>

Javascript 活动无效

Javascript Events Not Working

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