验证下拉选择，警告错误，导航回对话框

Question

如果用户未从下拉列表中选择有效的选项（“请选择”），我需要提醒用户“选择有效的拒绝原因”，并将其从出现的位置返回到对话框，而不提交更新。

用try-catch-throw编写的原始代码，我试图添加一个条件并抛出“请选择一个有效的原因”

试图删除try-catch-throw并添加var valid = true和条件检查

<table class="button">
<tr>
    <td>
<input type="submit" onclick="Save();return false;" value="Save" class="sButton">
<input type="button" onclick="Cancel();" value="Cancel" class="sButton">
    </td>
</tr>
</table>


function getReasons(ddlReason)
{
$.ajax({ 
   url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('Reason for Rejection')/Items?$orderby=Title", 
   type: "GET", 
   async: false,
   headers: {"accept": "application/json;odata=verbose"}, 
   success: function (data) { 
      if (data != undefined && data.d != undefined && data.d.results != undefined && data.d.results.length > 0) { 
      /////////////

    var option = document.createElement("option");
    option.text = "Please Select";
    option.value = "-1";
    ddlReason.appendChild(option);

        $.each(data.d.results, function( index, value ) 
        {
            var option = document.createElement("option");
            option.text = value.Title;
            option.value = value.Id;
            ddlReason.appendChild(option);
        });
    } 
   }, 
   error: function (xhr) { 
      alert(xhr.status + ': ' + xhr.statusText); 
   } 
}); 
}



function Save()
{
var valid = true;
SP.SOD.executeFunc("sp.js", 'SP.ClientContext', function()
{
//      try
    {
        var clientContext = SP.ClientContext.get_current();
        var web = clientContext.get_web();
        var oList = clientContext.get_web().get_lists().getByTitle('Invoice History');

        var itemCreateInfo = new SP.ListItemCreationInformation();
        var oListItem = oList.addItem(itemCreateInfo);  

        oListItem.set_item('InvoiceID', window.frameElement.dialogArgs.InvoiceID); 

    oListItem.set_item('Title',window.frameElement.dialogArgs.InvoiceNo); 
        oListItem.set_item('RejectionReason',$("#ddlRejection option:selected").text()); 
        oListItem.set_item('Description', $("#rejectionComment").val()); 

        oListItem.update();
        clientContext.executeQueryAsync(onQuerySucceeded, onQueryFailed);
        {
            if(RejectionReason == "Please Select")
            valid = false
        }
    }
    if(valid == false)
    {
    alert("Please select a valid Reason for Rejection");
//      catch(err)
    }
    {
//          alert(err.message);
    }
});
}

我认为我遇到的部分问题是创建此订单所需的顺序。