how do I Check if a checkbox is checked using jquery or javascript?

You should use .is(:checked) in jQuery code to check if checkbox is checked, so your code will be

if ($('#ChangeURL').is(':checked')) {
 //do something here
}

Using jQuery 1.6+

if ($('#ChangeURL').prop('checked')) {
    //Checked
}

OR using Javascript checked property of a checkbox

if(document.getElementById('ChangeURL').checked) {
    //Checked Code
} else {
    //Note checked
}

Here are the all possible jQuery method to check, Checkbox state

//here changeURL is Id of the element
$('#changeURL').is(":checked")

$('#changeURL').prop('checked')

$('#changeURL')[0].checked

$('#changeURL').get(0).checked