JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox"  checked id="c_b[]" name="c_b[]" value="1">
   <input type="checkbox"  id="c_b[]" name="c_b[]" value="2" checked>
   <input type="checkbox" value="3" id="c_b[]" name="c_b[]">

JavaScript

$(document).ready(function()
                  {
                     
var val = [];
    $(':checkbox:checked').each(function(i){
      val[i] = $(this).val();
    });
    alert(val);
                  });