let address = {
  street: '123 main st',
  city: 'springfield',
  state: 'idaho',
  zip: '12345'
}

let anotherAddressProp = 'street2'

address[anotherAddressProp] = "apt. 3B"
address.anotherAddressProp = "ste 500"

console.log(JSON.stringify(address, null, 2));