check checkbox checked or not in jquery code example

Example 1: How to check whether a checkbox is checked in 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
}

Example 2: jquery checkbox checked

$("checkbox").is(":checked")

Example 3: jquery check if checkbox is not checked

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

Example 4: check whether a checkbox is checked in jQuery

if ($('#grepperRocks').is(':checked')) {
	// this checkbox is checked
}

Example 5: how do i check if JQuery checkbox is checked

$('#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>

Example 6: jquery check if all checkbox is not checked

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