NU
//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
}
NU
<script type=text/javascript>
function validate(){
if (remember.checked == 1){
alert("checked") ;
} else {
alert("You didn't check it! Let me check it for you.")
}
}
</script>
<input id="remember" name="remember" type="checkbox" onclick="validate()" />