从类名中获取数字

Question

我有动态生成的 div 部分，类名以数字结尾。我想从类属性中获取数字

我想从类 submit-1 (1),submission-2 (2) 中获取数字，并像在代码段中一样尝试。我发现了错误未定义的匹配函数。如何从类属性中获取数字

$(document).ready(function(){

  var num = $('.submission-').attr('class').match(/\d+$/)[0];

  console.log(num);

});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>

<div class="webform submission-1">

   <span class="first">1</span>

   <span class="second">11</span> 

</div>

<div class="webform submission-2">

   <span class="first">2</span> 

   <span class="second">22</span> 

</div>

<div class="webform submission-3">

   <span class="first">3</span> 

   <span class="second">33</span>  

</div>

<div class="webform submission-4">

   <span class="first">4</span> 

   <span class="second">44</span>  

</div>

<div class="webform submission-12">

   <span class="first">12</span> 

    <span class="second">1212</span>  

</div>