get value of checked checkboxes jquery

//using plane javascript 
if(document.getElementById('on_or_off_checkbox').checked) {
    //I am checked
} 

//using jQuery
if($('#on_or_off_checkbox').is(':checked')){
    //I am checked
}

if ($('#check_id').is(":checked"))
{
  // it is checked
}

$(your_checkbox).is(':checked');

// Check a checkbox
$(selector).prop('checked', true);
// Un-check a checkbox
$(selector).prop('checked', false);
// Determine if checked or not
isChecked = $(selector).prop('checked');

console.log($('input[name="locationthemes"]:checked').serialize());

//or

$('input[name="locationthemes"]:checked').each(function() {
   console.log(this.value);
});

$('#isAgeSelected').click(function() {
    $("#txtAge").toggle(this.checked);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js">
  </script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">Age is something</div>

var checked = '0';  if($('#checkbox').prop('checked')){ checked = '1'; }

var values = $('input[name=grepperRocks]:checked')
               .map(() => { return this.value }).get();

$('#' + id).is(":checked")

$('input.checkbox').is(':checked')