example.js

function describe_object_array_manipulation_from_obj_values() {
  const obj_old = { uname: 'frank', value1: 9, value2: 12 }
  let obj_new = {}
  
  // check if uname key exists in object.
  console.log(!('uname' in obj_new)) // false

  // create an empty array of 2 for the values to eventually land.
  obj_new['uname'] = new Array(2)

  // now uname key should exist
  console.log(!('uname' in obj_new)) // true  
}

describe_object_array_manipulation_from_obj_values()

function describe_object_array_manipulation() {
  const obj_old = { uname: 'frank', value1: 9, value2: 12 }
  let obj_new = {}
  
  // check if uname key exists in object.
  console.log(!(obj_old.uname in obj_new)) // false

  // create an empty array of 2 for the values to eventually land.
  obj_new[obj_old.uname] = new Array(2)

  // now uname key should exist
  console.log(!(obj_old.uname in obj_new)) // true  
}

describe_object_array_manipulation()