how to push array to json object in angular : // i have an obj like below

    let obj = {staff_changes: []};

// testcase-1    success

    for (let i = 0; i < 4; i++) {
     obj.staff_changes.push({
      id: 'staff'+i
     });
    }

// testcase -2  failed

    let obj = {staff_changes: []};
    for (let i = 0; i < 4; i++) {
     obj.staff_changes.push({
      id: i,
      newStaff.push({
       id: 'staff'+i
      });
      
     });
    }
    console.log(obj);

in testcase2 i am trying to push an array with name 'newStaff' even it is not present in obj.
in console obj with 4 items is displaying but 'newStaff' is not pushing to obj.
it is my application requirement please help me