JAVASCRIPT

jquery check if checkbox is not checked

if (!$("#checkboxID").is(":checked")) {
    // do something if the checkbox is NOT checked
}

jquery checkbox checked or not

$('input[type="checkbox"]').click(function(){
            if($(this).is(":checked")){
                console.log("Checkbox is checked.");
            }
            else if($(this).is(":not(:checked)")){
                console.log("Checkbox is unchecked.");
            }
        });

jquery validate all checkbox checked

<form id="form1" action="/controller/action" method="post">
   <input type="checkbox" name="box1" class="cBox" />
   <input type="checkbox" name="box2" class="cBox" />
   <input type="checkbox" name="box3" class="cBox" />
  <input type="submit" value="Submit" />
</form>
<script>
$('#form1').submit(function() {
   if ($('input:checkbox', this).length == $('input:checked', this).length ) {
            // everything's fine...
   } else {
            alert('Please tick all checkboxes!');
            return false;
   }
});
</script>

jquery checkbox checked or not

<script>
    $(document).ready(function(){
        $('input[type="checkbox"]').click(function(){
            if($(this).prop("checked") == true){
                console.log("Checkbox is checked.");
            }
            else if($(this).prop("checked") == false){
                console.log("Checkbox is unchecked.");
            }
        });
    });

jquery check if all checkbox is not checked

 $('#checkAll').click(function () {    
     $('input:checkbox').prop('checked', this.checked);    
 });