正确的比较操作符是什么?如果仍然选择默认值0，则添加按钮不应该接受用户输入

Question

名称和电子邮件输入字段已经可以工作了，使用什么比较运算符或if else语句，以便如果仍然选择默认值0，用户无法继续，添加按钮将不接受输入?

$("#anchAddStudent").click(function() {
  var id = $('#last').val();
  console.log(id)
  var name = $('#inputName').val();
  var email = $('#inputEmail').val();
  var department_id = $('#selectDepartment').val();
  let last = $('#last').val()
  var data = {
    'name': $('#inputName').val(),
    'email': $('#inputEmail').val(),
    'department_id': $('#selectDepartment').val()
  }
  console.log(data);
  $.ajaxSetup({
    headers: {
      'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
    }
  });
  $.ajax({
    type: "POST",
    url: "/students",
    data: data,
    dataType: "json",
    success: function(response) {
      function IsEmail(email) {
        var regex = /^([a-zA-Z0-9_.-+])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/;
        if (!regex.test(email)) {
          return false;
        } else {
          return true;
        }
      }
      if (response.status == 400) {
        if (email.indexOf("@") < 0 || email.indexOf(".") < 0) {
          $("#spanInputEmail").removeClass('hideme');
          $("#inputEmail").addClass('borderColor');
        }
        if (name == "") {
          $("#spanInputName").removeClass('hideme');
          $("#inputName").addClass('borderColor');
        }
        if (department_id == 0) {
          $("#spanSelectDept").removeClass('hideme');
          console.log(department_id);
        }
      } else {
        $('#last').val(parseInt(last) + 1);
        $('#saveform_errList').html("");
        $('#success_message').addClass('alert alert-success');
        $('#success_message').text(response.message);
        $("#inputForm").find('input').val("");
        $("#inputName").val('');
        $("#inputEmail").val('');
        $("#selectDepartment").val('');
        // append row inside the table
        $("table tbody").append(
          `<tr>
                <td class='studentId'>${id}.</td>
                <td class='studentName'>${name}</td>
                <td class='studentEmail'>${email}</td>
                <td class='studentDept'>${response.dept_name}</td>
                <td class='studActions' data-studId='${response.id}' data-name='${name}' data-email='${email}' data-dept='${response.dept_name}' data-deptId='${department_id}' data-studDept='${department_id}'>
                <button type='button' value='${response.id}' data-id='{{ ${response.id} }}' class='btnDeleteStudent btn btn-danger btn-sm float-end'>Delete</button>
                <button type='button' class='btnEditStudent btn btn-primary btn-sm float-end'>Edit</button>
                <button type='button' class='btnCancelEditStudent btn btn-secondary btn-sm float-end hideme'>Cancel</button>
                <button type='button' class='btnUpdateStudent btn btn-primary btn-sm float-end                                hideme'>Update</button>
                </td>;
            </tr>`
        )
      }
    }
  });
});

名称和电子邮件输入字段已经工作了，如果仍然选择默认值0，则用户无法继续并且添加按钮将不接受输入，那么使用什么比较运算符或if else语句是正确的?在我的例子中，添加按钮仍然接受，即使它是默认的。我应该在代码中修改什么?请帮助

Answer 1

我认为您正在谈论department_id的值，如果它的值为零(0)，则不应进一步执行代码。你可以这样做并得到回报。像

function test() {
  var username = $('#username').val();
  var useremail = $('#useremail').val();
  var department_id = $('#department_id').val();
  alert(department_id);
  if(department_id == 0){
  //here you can write your code, that should execute if department_id is zero
          $("#demo").text('Sorry value is zero');
          return;
  }
  
  alert("Alert to execute after if condition, only if the if  condition does not run");
}
function showDepartment() {
    $('#demo').text(
    'department_id : '+ $('#department_id').val()
    );
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input id="username" type="text" placeholder='Enter name' /> <br>
<input id="useremail" type="email" placeholder='Enter Email' /> <br>
<select name="department" id="department_id" onchange="showDepartment()" >
  <option value="0" selected >Please Select</option>
  <option value="1">Department 1</option>
  <option value="2">Department 2</option>
  <option value="3">Department 3</option>
</select>
<br> 
<p id="demo"> </p>
<button onclick="test()"> Click Me </button>