Well, first of all, in JavaScript null is an object. There's another value for things that don't exist, undefined. The DOM returns null for almost all cases where it fails to find some structure in the document, but in JavaScript itself undefined is the value used. Second, no, they are not directly equivalent. If you …

Javascript 1var checkBoxContainer = $("#container"); 2var checkboxValueId = valueOfClickedCheckbox; 3var checkBox = checkBoxContainer.find("input[type=checkbox][value=" + checkboxValueId + "]"); 4var isChecked = checkBox.is(":checked"); 5 6if (checkboxValueId == 0) { 7 if (isChecked) 8 …