Question

它应该在控制台中说Bob Miller

但它代之以Undefined Undefined

如果有人帮我解决这个问题，我真的很感激。

<body bgcolor='000000'>
   <center>
       <input placeholder='Enter First Name' value='Bob' class='firstName'>
       <input placeholder='Enter Last Name' value='Miller' class='lastName'>
   </center>
</body>
<script>
   firstname = document.getElementsByClassName('firstName').value;
   lastname = document.getElementsByClassName('lastName').value;
   result = firstname + ' ' + lastname;
   console.log(result);
</script>

Answer 1

document.getElementsByClassName方法返回一个像对象这样的数组，而不是单个数组。您需要访问该对象中的[0]th项作为访问带索引的数组，然后获取其值。同时使用var/let/const关键字明确声明您的变量。

＆＃13;
＆＃13;
var firstname = document.getElementsByClassName('firstName')[0].value; // ---------------------------------------------------------^^^------ var lastname = document.getElementsByClassName('lastName')[0].value; // -------------------------------------------------------^^^------ var result = firstname + ' ' + lastname; console.log(result);
＆＃13;
<input placeholder='Enter First Name' value='Bob' class='firstName'> <input placeholder='Enter Last Name' value='Miller' class='lastName'>
＆＃13;
＆＃13;
＆＃13;

为什么不管Console.log结果？

1 个答案: