表单验证 - html 和 javascript

Question

我对编码比较陌生——处理表单验证，并且无法使用我的 formValidation 函数让页面实际返回 false（如果用户输入了不正确的 isbn 长度，则不提交表单）。想知道我在这里缺少什么。

无论 isbn.length 是什么，都会弹出警报并提交表单——但是，如果长度正确，它会被添加到数据库中并重新路由到主页。如果它不是正确的长度，它被路由到 “此页面无法正常工作 localhost 没有发送任何数据。 ERR_EMPTY_RESPONSE"

---

Javascript：

//function to validate the form's ISBN number input and ensure it's between 10-14 digits.

function formValidation(){
    var isbn = document.forms["sellForm"]["isbn"];

        if (isbn.length >= 10 && isbn.length <= 14){
         return true;

     }
     else
     {
         alert("Please input a 10-14 digit ISBN number");
         isbn.focus();
         return false;

     }
 }

</script>

对应的HTML：

<form name="sellForm" method="POST" action="/create" role="form" onsubmit="formValidation()">
              <div class="form-group">
                <label for="role" >ISBN</label>
                <input type="number" size=14 class="form-control" name="isbn" id="role"  required
               placeholder="input the 10-14 digit ISBN number"/>
              </div>

              <div class="form-group">
                  <label for="age">Condition</label>
                                    <br>
   <input type="radio" name="book_condition" value="Very Used"> Very Used<br>
     <input type="radio" name="book_condition" value="Lightly Used"> Lightly Used<br>
     <input type="radio" name="book_condition" value="Like New"> Like New
                  </div>
              </div>

              <div class="form-group">
                <label>Price</label>
                <input type="number" class="form-control" name="price" required
                                placeholder="input whole dollar price">
              </div>

              <button type="submit" class="btn btn-primary btn-md" id="add-btn">
                                <span class="fa fa-fire"></span> Sell</button>

            </form>

Answer 1

您可能需要像这样检查 isbn.value：

function formValidation(){
  var isbn = document.forms["sellForm"]["isbn"];

  if (isbn.value >= 10 && isbn.value <= 14) {
       return true;
  } else {
       alert("Please input a 10-12 digit ISBN number");
       isbn.focus();
       return false;
  }
}

然后根据需要添加逻辑。

Answer 2

您需要检查isbn 输入字段值的长度，并在表单标记中获取formValidation 函数在onsubmit 处理程序中的返回值，如下所示：onsubmit="return formValidation()"。

function formValidation(){
    var isbn = document.forms["sellForm"]["isbn"];
        // check for the input field value's length
        if (isbn.value.length >= 10 && isbn.value.length <= 14){
         return true;

     }
     else
     {
         alert("Please input a 10-12 digit ISBN number");
         isbn.focus();
         return false;

     }
 }

<form name="sellForm" method="POST" action="/create" role="form" onsubmit="return formValidation()">
              <div class="form-group">
                <label for="role" >ISBN</label>
                <input type="number" size=14 class="form-control" name="isbn" id="role"  required
               placeholder="input the 10-14 digit ISBN number"/>
              </div>

              <div class="form-group">
                  <label for="age">Condition</label>
                                    <br>
   <input type="radio" name="book_condition" value="Very Used"> Very Used<br>
     <input type="radio" name="book_condition" value="Lightly Used"> Lightly Used<br>
     <input type="radio" name="book_condition" value="Like New"> Like New
                  </div>
              </div>

              <div class="form-group">
                <label>Price</label>
                <input type="number" class="form-control" name="price" required
                                placeholder="input whole dollar price">
              </div>

              <button type="submit" class="btn btn-primary btn-md" id="add-btn">
                                <span class="fa fa-fire"></span> Sell</button>

            </form>

Answer 3

您还有其他问题（请参阅Andre's answer），但您需要将return 添加为onsubmit 属性的一部分

<form name="sellForm" method="POST" action="/create" role="form" onsubmit="return formValidation();">

完整版

function formValidation() {  
  /*This is the form element*/ 
  var isbnEl = document.forms["sellForm"]["isbn"];
  var isbn = isbnEl.value;
  
  /*The following 2 lines are for demonstration only and can be removed*/
  console.log(isbnEl);
  console.log(isbn);
  
  if (isbn.length >= 10 && isbn.length <= 14) {
    return true;

  } else {
    alert("Please input a 10-12 digit ISBN number");
    isbnEl.focus();
    return false;
  }
}

<form name="sellForm" method="POST" action="/create" role="form" onsubmit="return formValidation()">
  <div class="form-group">
    <label for="role">ISBN</label>
    <input type="number" size=14 class="form-control" name="isbn" id="role" required placeholder="input the 10-14 digit ISBN number" />
  </div>

  <div class="form-group">
    <label for="age">Condition</label>
    <br>
    <input type="radio" name="book_condition" value="Very Used"> Very Used<br>
    <input type="radio" name="book_condition" value="Lightly Used"> Lightly Used<br>
    <input type="radio" name="book_condition" value="Like New"> Like New
  </div>
  <!--</div> <---- This is an orphan tag, remove it -->

  <div class="form-group">
    <label>Price</label>
    <input type="number" class="form-control" name="price" required placeholder="input whole dollar price">
  </div>

  <button type="submit" class="btn btn-primary btn-md" id="add-btn">
                                <span class="fa fa-fire"></span> Sell</button>

</form>