Can't get checked checkboxes in jquery

I'm trying to fill an array but jquery isn't finding the checked checkboxes

$('input[name="frequency"]:checked').map(function() {
  frequencies.push($(this).val());
});

<div id="frequencyCheckboxes" class="btn-group" data-toggle="buttons" style="width:270px;">
  <label class="btn btn-primary" for="cbm">
    <input id="cbM" name="frequency" value="M" type="checkbox" autocomplete="off">M
  </label>
  <label class="btn btn-primary" for="cbW1">
    <input id="cbW1" name="frequency" value="W1" type="checkbox" autocomplete="off">W1
  </label>
  <label class="btn btn-primary" for="cbW2">
    <input id="cbW2" name="frequency" value="W2" type="checkbox" autocomplete="off">W2
  </label>
  <label class="btn btn-primary" for="cbW3">
    <input id="cbW3" name="frequency" value="W3" type="checkbox" autocomplete="off">W3
  </label>
  <label class="btn btn-primary" for="cbW4">
    <input id="cbW4" name="frequency" value="W4" type="checkbox" autocomplete="off">W4
  </label>
  <label class="btn btn-primary" for="cbW5">
    <input id="cbW5" name="frequency" value="W5" type="checkbox" autocomplete="off">W5
  </label>
</div>