表单验证-html和javascript

Question

我是编码表单验证方面的新手，无法使用formValidation函数使页面实际返回false（如果用户输入错误的isbn长度，则不提交表单）。 想知道我在这里想念的是什么。

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，它将被添加到数据库中并重新路由到主页。 如果长度不正确，则会路由到“此页面无法正常运行，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，并且在form标记中，您需要像这样在onsubmit处理程序中获取formValidation函数的返回值： 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的答案 ），但需要将return作为onsubmit属性的一部分添加

<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>