es6-spread.js

var state1 = {
  val1 : 'abc',
  val2: 'xyz'
};

var state2 = {
  val2 : 'mno',
  val3: 'xyz'
};

var state3 = { ...state1, ...state2}; //{val1: 'abc', val2: 'mno', val3: 'xyz'}