{
  id: 123,
  people: [{
      name: "Bob",
      age: 50
   }, {
      name: "Alice",
      age: 40
  }]
}

and

{
  id: 123,
  people: [{
      name: "Bob",
      age: 51 // bob is older now
   }, {
      name: "Alice",
      age: 40
  }]
}

sourceObject = updatedCopiedObject;

Object.assign(sourceObject, updatedCopiedObject);