how to loop through nested json object and assign to another class instance

I am looping to object data in Angular 5 app and assigning value to another class object instance. I have also nested data object and even sub-nested, I need to know how to loop these nested values to identify and assign to another object instance.

In following example, options:[] part is hard code and I need to loop here

 for(var key in questionsList)

  let questionElementType = questionsList[key].questionElement.questionElementType[0].typeDefination;      


    let _dropBox = new DropdownQuestion({
      consultationId: questionsList[key].consultationId,
      questionId: questionsList[key].questionId,
      questionElementId: questionsList[key].questionElementId,          
      questionType: questionsList[key].questionType,
      key: questionsList[key].questionId,    
      label: questionsList[key].title,
      options: [                //need help here, how to loop nested object
        {key: 'solid',  value: 'Solid'},
        {key: 'great',  value: 'Great'},
        {key: 'good',   value: 'Good'},
        {key: 'unproven', value: 'Unproven'}
      order: 1
  //other control type here i.e. checkbox, textbox, radio etc

JSON array structure

enter image description here

I believe, it require to loop data unless there is better way to do it?