const food = { beef: '🥩', bacon: '🥓' }
//shallow copy
1.// "Spread" => 
{ ...food }
2.// "Object.assign" => shallow copy 
Object.assign({}, food)
// deep copy when object consists nested objects and arrays
3. // "JSON" => convert to string and parse back
JSON.parse(JSON.stringify(food))
// RESULT:
// { beef: '🥩', bacon: '🥓' }
4.// deep copy by using iterator
function iterationCopy(src) {
  src = { beef: '🥩', bacon: '🥓' , num:[1,2,3,]}
  let target = {};
  for (let prop in src) {
    if (src.hasOwnProperty(prop)) {
      // if the value is a nested object, recursively copy all it's properties
      if (isObject(src[prop])) {
        target[prop] = iterationCopy(src[prop]);
      } else {
        target[prop] = src[prop];
      }
    }
  }
  return target;
}