Hello,
In JavaScript, the checked property sets or returns the checked state of a checkbox.
This property reflects the HTML checked attribute.
To check null in JavaScript, use triple equals operator(===) or Object.is() method. To find the difference between null and undefined, use the triple equality operator or Object.is() method.
The methods checkIndex, uncheckIndex, checkItem, unchecked and the event checkChange may be helpful to you. You can learn more about them in jqxDropDownList’s API Documentation.
Best Regards,