JavaScript 检查是否选择了 Select 选项

Question

我在表单页面上有一个 select 元素，如果用户尝试提交而不进行选择，我希望 label 的内部 html 更改。 这是 html。

  <div class="form-group">
    <label for="FamilySize" name = "FamSizeLable">How Many in Your Household</label>
    <select class="form-control" name = "FamilySize" id="FamilySize">
      <option disabled selected value="">Size</option>
      <option>1</option>
      <option>2</option>
      <option>3</option>
      <option>4</option>
      <option>5</option>
      <option>Good god ya'll</option>
    </select>
  </div>

我尝试过以几种不同的方式获取价值。

  else if(!document.getElementById("FamilySize").value){
    document.getElementByName("FamSizeLabel").innerHTML = "***You Must Select a Family Size***";
    document.getElementById("FamSizeLabel").style.color = "red";
    return false;
  }

和

  else if(!document.querySelector('[id = "FamilySize"]').value){
    document.getElementByName("FamSizeLabel").innerHTML = "***You Must Select a Family Size***";
    document.getElementById("FamSizeLabel").style.color = "red";
    return false;
  }

和

  else if(document.querySelector('[id = "FamilySize"]').value==null){
    document.getElementByName("FamSizeLabel").innerHTML = "***You Must Select a Family Size***";
    document.getElementById("FamSizeLabel").style.color = "red";
    return false;
  }

和

  else if(document.querySelector('[id = "FamilySize"]').value==""){
    document.getElementByName("FamSizeLabel").innerHTML = "***You Must Select a Family Size***";
    document.getElementById("FamSizeLabel").style.color = "red";
    return false;
  }

我还尝试在开发人员视图中使用 console.log 来查看我缺少的内容。 但是，我在 JavaScript 上是个菜鸟，似乎无法确定。 未选择 FamilySize 时仍会提交表单。 我可以赶上这个服务器端，但我想在 JavaScript 上做得更好，所以想弄清楚/理解这一点。

编辑（页面的完整代码如下）：

{% extends "layout.html" %}

{% block main %}
<!--form action tells this form what route to post the data to. DOH! -->
<form action="/form" method="post">
  <div class="form-group">
    <!--for="FormControlInput1"This was in the EmailLablel label not sure what it does-->
    <label id = "EmailLabel" >Email address</label>
    <input type="email" class="form-control" name = "Email" autocomplete = "off" autofocus id="FormControlInput1" placeholder="name@example.com">
  </div>
  <div class="form-group">
    <label id = "Fname" >First Name</label>
    <input type="text" class="form-control" name = "Fname" autocomplete = "off"  id="FnameFormControlInput" placeholder="John">
  </div>
  <div class="form-group">
    <label id = "Lname" >Last Name</label>
    <input type="text" class="form-control" name ="Lname" autocomplete = "off"  id="LnameFormControlInput" placeholder="Doe">
  </div>
  <div class="form-group">
    <label for="FamilySize" name = "FamSizeLable">How Many in Your Household</label>
    <select class="form-control" name = "FamilySize" id="FamilySize">
      <option disabled selected value="">Size</option>
      <option>1</option>
      <option>2</option>
      <option>3</option>
      <option>4</option>
      <option>5</option>
      <option>Good god ya'll</option>
    </select>
  </div>
  <div class="form-group">
    <label for="AgeGroup">Select Age Group</label>
    <select multiple class="form-control" name = "AgeGroup" id="AgeGroup">
      <option>0-15</option>
      <option>16-24</option>
      <option>25-36</option>
      <option>37-45</option>
      <option>45-Dead</option>
    </select>
  </div>
  <div class="form-group">
    <label for="Comments">Comments</label>
    <textarea class="form-control" name = "Comments" id="Comments" rows="3"></textarea>
  </div>
  <div class="form-check">
    <input type="checkbox" class="form-check-input" id="exampleCheck1">
    <label class="form-check-label" for="exampleCheck1">Check me out</label>
  </div>
  <button class="btn btn-primary" type="submit">Submit</button>
</form>

<script>

    document.querySelector('form').onsubmit=function(){
      if(!document.querySelector('[type = "email"]').value){
        document.getElementById("EmailLabel").innerHTML = "***You Must Provide an Email address***";
        document.getElementById("EmailLabel").style.color = "red";
        return false;
      }
      else if(!document.querySelector('[id = "FnameFormControlInput"]').value){
        document.getElementById("Fname").innerHTML = "***You Must Provide a First Name***";
        document.getElementById("Fname").style.color = "red";
        return false;
      }
      else if(!document.querySelector('[id = "LnameFormControlInput"]').value){
        document.getElementById("Lname").innerHTML = "***You Must Provide a Last Name***";
        document.getElementById("Lname").style.color = "red";
        return false;
      }
      // //Here we have to use label for family size because there is no text on the control itself
      else if(!document.getElementById("FamilySize").value){
        document.getElementByName("FamSizeLabel").innerHTML = "***You Must Select a Family Size***";
        document.getElementById("FamSizeLabel").style.color = "red";
        console.log(document.querySelector('[id = "FamilySize"]').value);
        return false;
      }
      else if(!document.querySelector('[id = "AgeGroup"]').value){
        document.getElementById("AgeGroup").innerHTML = "***You Select Your Age Group***";
        document.getElementById("AgeGroup").style.color = "red";
        return false;
      }
      alert(document.querySelector('[id = "FamilySize"]').value);
      return true;

    };
</script>
{% endblock %}

Answer 1

我已经编辑了我的原始帖子，并包含了您的一些进一步的输入元素。 我目前使用 class form-control来决定必须检查哪些元素（您当然可以使用另一个专门用于此目的的 class 名称）。 然后我 go 并使用返回整体 boolean 值的Array.reduce()方法检查它们。 根据该值是否会发生进一步的处理......

为了简化错误处理，我使用每个测试变量的名称来显示错误消息，该错误消息显示在每个输入元素之后的额外 div 中。

 var chk=Array.from(document.querySelectorAll('.form-control')), msg="You must enter a value for "; document.querySelector('#subm').addEventListener('click', function(){ if (chk.reduce(function(ac,el){ el.parentNode.querySelector('div.error').innerHTML= el.value==""? msg+el.name: ""; return ac || el.value==""}, false)) return false; console.log('OK, your data will be submitted...'); // and further code... })

 div.error {color: red;}

 <div class="form-group"> <label id = "EmailLabel" >Email address</label> <input type="email" class="form-control" name="Email" autocomplete = "off" autofocus id="FormControlInput1" placeholder="name@example.com"><div class="error"></div> </div> <div class="form-group"> <label id = "Fname" >First Name</label> <input type="text" class="form-control" name = "Fname" autocomplete = "off" id="FnameFormControlInput" placeholder="John"><div class="error"></div> </div> <div class="form-group"> <label id = "Lname" >Last Name</label> <input type="text" class="form-control" name ="Lname" autocomplete = "off" id="LnameFormControlInput" placeholder="Doe"><div class="error"></div> </div> <div class="form-group"> <label for="FamilySize">How Many in Your Household</label> <select class="form-control" name="FamilySize" id="FamilySize"> <option disabled selected value="">Size</option> <option>1</option> <option>2</option> <option>3</option> <option>4</option> <option>5</option> <option>Good god ya'll</option> </select><div class="error"></div> </div> <div class="form-group"> <label for="AgeGroup">Select Age Group</label> <select multiple class="form-control" name="AgeGroup" id="AgeGroup"> <option>0-15</option> <option>16-24</option> <option>25-36</option> <option>37-45</option> <option>45-Dead</option> </select><div class="error"></div> </div> <button id="subm">submit</button>

Answer 2

要访问选定的元素值或它的 innerHTML 类似这样的操作：

var e = document.getElementById("FamilySize");
// For the option tag value attribute:
var value = e.options[e.selectedIndex].value;
// For the option text:
var text = e.options[e.selectedIndex].text;

getElementsByName 方法没有单一选项。 要访问 label 的内容，您应该使用：

var labelInnerHTML = document.getElementsByName("FamSizeLable")[0].innerHTML

另请注意，您的代码中有拼写错误：

name = "FamSizeLable"

应该：

name = "FamSizeLabel"

Answer 3

我终于通过给我的 label 一个 id 解决了这个问题

  <div class="form-group">
  <label for="FamilySize" name = "FamSizeLable" id = "FamSizeLable">How Many in Your Household</label>
  <select class="form-control" name="FamilySize" id="FamilySize">
      <option disabled selected value="">Size</option>
      <option>1</option>
      <option>2</option>
      <option>3</option>
      <option>4</option>
      <option>5</option>
      <option>Good god ya'll</option>
    </select>
  </div>

然后将我的 JavaScript 修改为 select 选择器的 id 并检查""的值：

  else if(document.querySelector('#FamilySize').value==""){
    //Here the # means id
    document.querySelector('#FamSizeLable').innerHTML = "***You Must Select a Family Size***";
    document.querySelector('#FamSizeLable').style.color = "red";
    return false;
  }

Answer 4

您还需要像<option value="1">1</option>这样的值，然后将 0 值赋予 size 并检查 value 是否为 0 不允许用户继续。