Spread Property ↔ Enhanced Object Literals to add object property via Spread Operator

overlap Property Key with Spread Property will overwrite last property similar to overlapping Selector Style Rule

all Values spreadable including null & undefined (which result in {} )

!snippet Enhanced Object Literals with Spread Operator

const abc = {
  a: 1,
  b: {
    c: 3
  }
}

const abcd = {
  ...abc,
  d: 4
}

References