How to watch a inner variable of custom question type in SurveyJS?

question

I have defined a customer question type named cascadedropdown, the code is as follows :

ComponentCollection.Instance.add({
  // A unique name; must use lowercase
  name: 'casecadedropdown', // A display name used in the Toolbox
  title: 'casecade dropdown', // A default title for questions created with this question type
  defaultQuestionTitle: 'choose an option',
  elementsJSON: [{
      type: 'dropdown',
      name: 'question1',
      title: 'question1',
      choices: levelOneArray, 
 },{
      type: 'dropdown',
      name: 'question2',
      title: 'question2',
      startWithNewLine: false,
      choices:[],
 },{
      type: 'dropdown',
      name: 'question3',
      title: 'question3',
      startWithNewLine: false,
      choices:[],
      visible: {questionListLen} > 2
 },{
      type: 'dropdown',
      name: 'question4',
      title: 'question4',
      startWithNewLine: false,
      choices:[],
      visible: {questionListLen} > 3
 }
 ],
    calculatedValues:[{
        name:"questionListLen",
        expression: casecadeQuestionList.length
 } ],
  inheritBaseProps: true,
}]

after the cascadedropdown loading, the casecadeQuestionList will be assigned by another value, whether the question3 and question4 display or not depends on the casecadeQuestionList.length, how can I watch the casecadeQuestionList.length change?

trying
I defined the calculated value above, but it does not work. What should I do?