test.js

function textFieldEnteredHandler(enteredField) {

    if (enteredField.textField.type === "CHECKFORMFIELD")
    {
        TXTextControl.formFields.getItem(function(checkFormField) {
            checkFormField.getChecked(function(checked) {
                checkFormField.setChecked(!checked);
            })
        })
    }
}

TXTextControl.addEventListener("textFieldEntered", textFieldEnteredHandler);