Is there a way to clone an array which is nested inside another array in an object

Question

I have an obj that looks like this.

let obj= {
  title:"my form",
  endTIme:"2/20/22",
  mainList:[
    {
      type:"multiple", 
      checked:false,
      multiple:[
         {
           optionCheck: false,
           optionAnswer:""
         }
      ]
    }
  ]
}

I also have a button that every time I click, I want the obj fields to retain all its values only that the multiple array field should append a new object . But I cant seem to figure it out. Please I really need help

I tried cloning using spread operator and I wasn't getting the result I want as I learnt that spread operator is best used for shallow cloning

let newObj= {
 ...obj
  mainList:[
     ...obj.mainList,
    {
      multiple:[
         {
           optionCheck: false,
           optionAnswer:""
         }
      ]
    }
  ]
}

And this ends up duplicating the mainList instead.

What I want my result to like is this when I click the button once.

let obj = {
  title: "my form",
  endTIme: "2/20/22",
  mainList: [{
    type: "multiple",
    checked: false,
    multiple: [
    {
      optionCheck: false,
      optionAnswer: ""
    }, 
    {
      optionCheck: false,
      optionAnswer: ""
    }]
  }]
};

Answer 1

Just use array.push

let obj= {
  title:"my form",
  endTIme:"2/20/22",
  mainList:[
    {
      type:"multiple", 
      checked:false,
      multiple:[
         {
           optionCheck: false,
           optionAnswer:""
         }
      ]
    }
  ]
}

obj.mainList[0].multiple.push( {
           optionCheck: false,
           optionAnswer:""
         });
         
console.log(obj)