Попробуйте это
$(document).ready(function(){
var classes = $('[class*=submission]').map(function(_,cl) {
return cl.className.split(" ")[1].split("-")[1]; // or just cl.className.split("-")[1];
}).get();
console.log(classes);
})
<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>
Рекомендация - используйте атрибуты данных вместо, если вы можете изменить код сервера:
$(document).ready(function(){
var classes = $('[data-submission]').map(function(_,sub) {
return $(this).data("submission");
}).get();
console.log(classes);
})
<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" data-submission="2">
<span class="first">2</span>
<span class="second">22</span>
</div>
<div class="webform" data-submission="3">
<span class="first">3</span>
<span class="second">33</span>
</div>
<div class="webform" data-submission="4">
<span class="first">4</span>
<span class="second">44</span>
</div>
<div class="webform" data-submission="12">
<span class="first">12</span>
<span class="second">1212</span>
</div>