let oldProps = null;
function shallowCompare (props){
  if(props !== oldProps) console.log(props);
}

const john = { name: "john", age: 30 };

shallowCompare(john) // prints -> { name: "john", age: 30 }

const johnClone = {...john};
johnClone.age=31;
shallowCompare(johnClone) // prints -> { name: "john", age: 31 }