確定數據是否已經在選擇列表

Question

我有一個選擇定義爲 -

<div class="form-group"> 
    <div class="col-md-10"> 
    <select name="selected-attendees" id="selected-attendees" class="form-control" multiple size="5"> 
     @foreach (Customer attendee in Model.AttendeeList) 
     { 
      var attendeeName = String.Format("{0}, {1}", attendee.FullName, attendee.Email); 
      <option class="selectable-option" value="@attendee.Id">@attendeeName</option> 
     } 
    </select> 
    </div> 
</div> 

當用戶點擊添加按鈕，這是行動 -

$('#attendees-btn-add').click(function() { 
    if ($('#selectedAttendee').val() == '') { 
    alert("Select a customer to be added to the attendee list."); 
    } else { 
    $('#selected-attendees').append($('<option>', { 
     class: 'selectable-option', 
     value: $('#attendeeId').val(), 
     text: $('#selectedAttendee').val() 
     })); 
     $('#selectedAttendee').val(""); 
     $('#attendeeId').val(""); 
    } 
    }); 

我需要確定該用戶已被添加到選擇並顯示一條消息。

Answer 1

您可以用特定的值<option>查詢，並顯示該消息，如果有任何結果：

if ($('#selected-attendees option[value="' + $('#attendeeId').val() + '"]').length) { 
    //display message about duplicate 
} 

Answer 2

試試這個條件.click功能：在這裏

var exists = $("#selected-attendees").find('option[value=' + $('#attendeeId').val() + ']').length >0; 

    if(exists) 
    { 
    //do if exists 
    } 
    else 
    { 
    //do because not exists 
    } 

演示：http://jsfiddle.net/csdtesting/q9L59gmc/