https://medium.com/@michaelmcshinsky/merging-javascript-objects-b89af94d5b59

merging-javascript-objects-3.js

let obj1 = { firstName: 'John', lastName: 'Doe', email: 'johnydoe1@domain.com' };

let obj2 = { email: 'john.doe@domain.com', phone: '012–345–6789' };

let obj3 = { city: 'Salt Lake City', state: 'Utah' }

function merge(…arr) {
  return arr.reduce((acc, cur) => {
    // Can add custom logic for how keys or nested values should be handled.
    for (let key in cur) {
      acc[key] = cur[key];
    }
    return acc;
  }, {});
}

let newObj = merge(obj1, obj2, obj3);

// {
//  firstName: 'John',
//  lastName: 'Doe',
//  email: 'john.doe@email.com',
//  phone: '012–345–6789',
//  city: 'Salt Lake City',
//  state: 'Utah'
// }