如何向 Carbon 日期对象添加动态天数

How can I add dynamic number of days to a Carbon date object

请问我如何操作 Carbon 日期对象以将当前月份的天数添加到日期对象本身。
我有以下 html 形式:

<form method="POST">
   @csrf
   <input type="hidden" name="plan" id="plan" />
   <div class="form-group">
     <h5>@lang('Enter Invest Amount')</h5>
     <div class="input-group-append">
       <input type="text" name="amount" class="form-control" />
         <span class="input-group-text">{{ $general->cur_text }}</span>
     </div>
     <br>
     <h5>@lang('Select Investment End Date')</h5>
     <div class="input-group-append">
       <input type="text" name="investmentEndDate" class="investmentEndDate form-control"/>
     </div>
   </div>
   <div class="form-group">
     <button type="submit" class="btn btn--base" style="width:100%;">@lang('Invest')</button>
   </div>
</form>

然后Javascript:

const date = new Date();
const daysInTheMonth = new Date(date.getFullYear(), date.getMonth(), 0).getDate();
$(function () {
   $('.investmentEndDate').datepicker({
       minDate: daysInTheMonth
   });
   $('.planModal').on('click', function() {
     $('#depoModal #plan').val($(this).data('plan'));
   });
});

然后在我的 controller:UserController class 中,我有:

public function postplan(Request $request)
{

    $today = Carbon::now();
    $endDate = $today->addDays($today->daysInMonth);//emphasis here - it keeps returning today's date

    $request->validate([
        'plan' => 'required|numeric|exists:plans,id',
        'amount' => 'required|numeric|min:1',
        'investmentEndDate' => 'required|date|after_or_equal:'.$endDate
    ]);

    var_dump($endDate);//returns today's date 
    
    //other code ....
 }

当我提交表格时,日期没有按预期显示。我想将当月的天数添加到日期对象,但它一直返回今天的日期而不是当前日期 + 31 天,这应该给我 2021-09-14。
请问我做错了什么?

你不需要在另一个变量中分配它。 addDays() 修改当前 Carbon 对象。

public function postplan(Request $request)
{

    $today = Carbon::now();
    $today->addDays($today->daysInMonth);

    $request->validate([
        'plan' => 'required|numeric|exists:plans,id',
        'amount' => 'required|numeric|min:1',
        'investmentEndDate' => 'required|date|after_or_equal:'.$endDate
    ]);

    var_dump($today);// this will be at the date of one month later
    
    //other code ....
 }