how to check whether the checkbox is checked or not 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: checkbox is not getting checked

<input type="checkbox" name="free" value="mon09" onClick="this.checked=!this.checked;">

Example 3: check whether a checkbox is checked in jQuery

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

Example 4: if checkbox is checked

if ($('#id_input').is(':checked')) { }