if checkbox is checked

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

var checkBox = document.getElementById(id_field);
			if (checkBox.checked== true){
            }

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

if (document.getElementById('id of the check box here').checked) {
	// it is checked. Do something
} else {
	// it isn't checked. Do something else
}

if ($('input[name="transport"]').is(':checked')) {
	alert('checked');
	alert($(this).attr('id')); //To get ID of checkBox
}

function checkAddress()
{
    var chkBox = document.getElementById('checkAddress');
    if (chkBox.checked)
    {
        // ..
    }
}