javascript - 如何使用 JS 验证元素是否存在于表单中

Question

<pre>
<script>
// here i want to check form validation
//if i use for loop txtbox2 is not exist in my form so i am getting Js error


//Don't write individual validation
//check element is exist or not if exist check for validation

//I need know how to check an element is exist or not
</script>

<form
<input type="text" id="txtbox1" name="txtbox1" />*
<input type="text" id="txtbox3" name="txtbox3" />*
<input type="text" id="txtbox4" name="txtbox4" />*
<input type="text" id="txtbox5" name="txtbox5" />*
<input type="text" id="txtbox15" name="txtbox15" />*
<input type="text" id="txtbox28" name="txtbox28" />*

</pre>

Answer 1

对它们应用一个类:

<input type="text" id="txtbox1" name="txtbox1" class="txt" />
<input type="text" id="txtbox3" name="txtbox3" class="txt" />
<input type="text" id="txtbox4" name="txtbox4" class="txt" />
<input type="text" id="txtbox5" name="txtbox5" class="txt" />
<input type="text" id="txtbox15" name="txtbox15" class="txt" />
<input type="text" id="txtbox28" name="txtbox28" class="txt" />

然后像这样:

function validate(){
  var elms = document.getElementsByTagName('input');

  for (var i = 0; i < elms.length; i++){
    if (elms[i].className === 'txt'){
      if (elms[i].value === ''){
          alert('Make sure to fill in all required fields');
          // now focus it
          elms[i].focus();
          return false;
      }
    }
  }

  return true;
}

然后像这样调用上面的函数:

<form ............ onsubmit="return validate();">